Abrikosov, Igor
Overview
Works:  109 works in 110 publications in 2 languages and 111 library holdings 

Roles:  the, Author, Thesis advisor, Opponent 
Publication Timeline
.
Most widely held works by
Igor Abrikosov
Comparison of thermodynamic properties of cubic Cr 1x Al x N and Ti 1x Al x N from firstprinciples calculations by
Björn Alling(
)
1 edition published in 2007 in English and held by 2 WorldCat member libraries worldwide
In order to investigate the stability of the cubic phase of Cr 1− x Al x N at high AlN content, first principles calculations of magnetic properties, lattice parameters, electronic structure, and mixing enthalpies of the system were performed. The mixing enthalpy was calculated on a fine concentration mesh to make possible the accurate determination of its second concentration derivative. The results are compared to calculations performed for the related compound Ti 1− x Al x N and with experiments. The mixing enthalpy is discussed in the context of isostructural spinodal decomposition. It is shown that the magnetism is the key to understand the difference between the Cr and Ticontaining systems. Cr 1− x Al x N turns out to be more stable against spinodal decomposition than Ti 1− x Al x N , especially for AlNrich samples which are of interest in cutting tools applications
1 edition published in 2007 in English and held by 2 WorldCat member libraries worldwide
In order to investigate the stability of the cubic phase of Cr 1− x Al x N at high AlN content, first principles calculations of magnetic properties, lattice parameters, electronic structure, and mixing enthalpies of the system were performed. The mixing enthalpy was calculated on a fine concentration mesh to make possible the accurate determination of its second concentration derivative. The results are compared to calculations performed for the related compound Ti 1− x Al x N and with experiments. The mixing enthalpy is discussed in the context of isostructural spinodal decomposition. It is shown that the magnetism is the key to understand the difference between the Cr and Ticontaining systems. Cr 1− x Al x N turns out to be more stable against spinodal decomposition than Ti 1− x Al x N , especially for AlNrich samples which are of interest in cutting tools applications
MAX IV : conceptual design report(
Book
)
2 editions published in 2006 in Swedish and held by 2 WorldCat member libraries worldwide
2 editions published in 2006 in Swedish and held by 2 WorldCat member libraries worldwide
Dipolar spin relaxation of divacancy qubits in silicon carbide by Oscar Bulancea Lindvall(
)
1 edition published in 2021 in English and held by 1 WorldCat member library worldwide
Divacancy spins implement qubits with outstanding characteristics and capabilities in an industrial semiconductor host. On the other hand, there are still numerous open questions about the physics of these important defects, for instance, spin relaxation has not been thoroughly studied yet. Here, we carry out a theoretical study on environmental spininduced spin relaxation processes of divacancy qubits in the 4H polytype of silicon carbide (4HSiC). We reveal all the relevant magnetic field values where the longitudinal spin relaxation time T1 drops resonantly due to the coupling to either nuclear spins or electron spins. We quantitatively analyze the dependence of the T1 time on the concentration of point defect spins and the applied magnetic field and provide an analytical expression. We demonstrate that dipolar spin relaxation plays a significant role both in asgrown and ionimplanted samples and it often limits the coherence time of divacancy qubits in 4HSiC
1 edition published in 2021 in English and held by 1 WorldCat member library worldwide
Divacancy spins implement qubits with outstanding characteristics and capabilities in an industrial semiconductor host. On the other hand, there are still numerous open questions about the physics of these important defects, for instance, spin relaxation has not been thoroughly studied yet. Here, we carry out a theoretical study on environmental spininduced spin relaxation processes of divacancy qubits in the 4H polytype of silicon carbide (4HSiC). We reveal all the relevant magnetic field values where the longitudinal spin relaxation time T1 drops resonantly due to the coupling to either nuclear spins or electron spins. We quantitatively analyze the dependence of the T1 time on the concentration of point defect spins and the applied magnetic field and provide an analytical expression. We demonstrate that dipolar spin relaxation plays a significant role both in asgrown and ionimplanted samples and it often limits the coherence time of divacancy qubits in 4HSiC
Synthesis of Ti3AuC2, Ti3Au2C2 and Ti3IrC2 by noble metal substitution reaction in Ti3SiC2 for hightemperaturestable Ohmic
contacts to SiC by Hossein Fashandi(
)
1 edition published in 2017 in English and held by 1 WorldCat member library worldwide
The large class of layered ceramics encompasses both van der Waals (vdW) and nonvdW solids. While intercalation of noble metals in vdW solids is known, formation of compounds by incorporation of noblemetal layers in nonvdW layered solids is largely unexplored. Here, we show formation of Ti3AuC2 and Ti3Au2C2 phases with up to 31% lattice swelling by a substitutional solidstate reaction of Au into Ti3SiC2 singlecrystal thin films with simultaneous outdiffusion of Si. Ti3IrC2 is subsequently produced by a substitution reaction of Ir for Au in Ti3Au2C2. These phases form Ohmic electrical contacts to SiC and remain stable after 1,000 h of ageing at 600 degrees C in air. The present results, by combined analytical electron microscopy and ab initio calculations, open avenues for processing of noblemetalcontaining layered ceramics that have not been synthesized from elemental sources, along with tunable properties such as stable electrical contacts for hightemperature power electronics or gas sensors
1 edition published in 2017 in English and held by 1 WorldCat member library worldwide
The large class of layered ceramics encompasses both van der Waals (vdW) and nonvdW solids. While intercalation of noble metals in vdW solids is known, formation of compounds by incorporation of noblemetal layers in nonvdW layered solids is largely unexplored. Here, we show formation of Ti3AuC2 and Ti3Au2C2 phases with up to 31% lattice swelling by a substitutional solidstate reaction of Au into Ti3SiC2 singlecrystal thin films with simultaneous outdiffusion of Si. Ti3IrC2 is subsequently produced by a substitution reaction of Ir for Au in Ti3Au2C2. These phases form Ohmic electrical contacts to SiC and remain stable after 1,000 h of ageing at 600 degrees C in air. The present results, by combined analytical electron microscopy and ab initio calculations, open avenues for processing of noblemetalcontaining layered ceramics that have not been synthesized from elemental sources, along with tunable properties such as stable electrical contacts for hightemperature power electronics or gas sensors
Missingatom structure of diamond Sigma 5 (001) twist grain boundary by
Peter Steneteg(
)
1 edition published in 2011 in English and held by 1 WorldCat member library worldwide
We carried out a combined experimental and theoretical study of grain boundaries in polycrystalline diamond, aimed at achieving the conditions in which grain boundaries are equilibrated. Raman spectra of compacted at highpressure and hightemperature diamond powders allow us to identify signals from sp(2)bonded atoms, in addition to a strong peak at 1332 cm( 1), corresponding to sp(3)bonded carbon. To verify our interpretation of the experiment, Sigma 5 (001) twist grain boundaries of polycrystalline diamond were studied by means of molecular dynamics simulations using the technique proposed by von Alfthan et al. [Phys. Rev. Lett. 96, 055505 (2006)]. We find that grainboundary (GB) configurations, from which one atom is removed, have significantly lower energy compared to those obtained with conventional techniques. These calculated GBs are highly ordered, a few monolayers thick, in agreement with experimental observations, and are primarily sp(2) bonded. This paper underlines the importance of varying the number of atoms within GBs in molecular dynamics simulations to correctly predict the GB groundstate structure
1 edition published in 2011 in English and held by 1 WorldCat member library worldwide
We carried out a combined experimental and theoretical study of grain boundaries in polycrystalline diamond, aimed at achieving the conditions in which grain boundaries are equilibrated. Raman spectra of compacted at highpressure and hightemperature diamond powders allow us to identify signals from sp(2)bonded atoms, in addition to a strong peak at 1332 cm( 1), corresponding to sp(3)bonded carbon. To verify our interpretation of the experiment, Sigma 5 (001) twist grain boundaries of polycrystalline diamond were studied by means of molecular dynamics simulations using the technique proposed by von Alfthan et al. [Phys. Rev. Lett. 96, 055505 (2006)]. We find that grainboundary (GB) configurations, from which one atom is removed, have significantly lower energy compared to those obtained with conventional techniques. These calculated GBs are highly ordered, a few monolayers thick, in agreement with experimental observations, and are primarily sp(2) bonded. This paper underlines the importance of varying the number of atoms within GBs in molecular dynamics simulations to correctly predict the GB groundstate structure
Strong electron correlations stabilize paramagnetic cubic Cr1xAlxN solid solutions by
Björn Alling(
)
1 edition published in 2013 in English and held by 1 WorldCat member library worldwide
The stability of rock salt structure cubic Cr1xAlxN solid solutions at high Al content and high temperature has made it one of the most important materials systems for protective coating applications. We show that the strong electron correlations in a material with dynamic magnetic disorder is the underlying reason for the observed stability against isostructural decomposition. This is done by using the firstprinciples disordered local moments molecular dynamics technique, which allows us to simultaneously consider electronic, magnetic, and vibrational degrees of freedom
1 edition published in 2013 in English and held by 1 WorldCat member library worldwide
The stability of rock salt structure cubic Cr1xAlxN solid solutions at high Al content and high temperature has made it one of the most important materials systems for protective coating applications. We show that the strong electron correlations in a material with dynamic magnetic disorder is the underlying reason for the observed stability against isostructural decomposition. This is done by using the firstprinciples disordered local moments molecular dynamics technique, which allows us to simultaneously consider electronic, magnetic, and vibrational degrees of freedom
Electronelectron scattering and thermal conductivity of epsiloniron at Earths core conditions by L. V Pourovskii(
)
1 edition published in 2017 in English and held by 1 WorldCat member library worldwide
The electronic state and transport properties of hot dense iron are of the utmost importance for the understanding of Earths interior. Combining stateoftheart density functional and dynamical mean field theories we study the impact of electron correlations on the electrical and thermal resistivity of hexagonal closepacked epsilonFe at Earths core conditions and show that the electronelectron scattering in epsilonFe exhibit a nearly perfect Fermiliquid (FL) behavior. Accordingly, the quadratic dependence of the scattering rate, typical of FLs, leads to a modification of the WiedemannFranz law and suppresses the thermal conductivity with respect to the electrical one. The consequence is a significant increase of the electronelectron thermal resistivity, which is found to be of comparable magnitude to the electronphonon one
1 edition published in 2017 in English and held by 1 WorldCat member library worldwide
The electronic state and transport properties of hot dense iron are of the utmost importance for the understanding of Earths interior. Combining stateoftheart density functional and dynamical mean field theories we study the impact of electron correlations on the electrical and thermal resistivity of hexagonal closepacked epsilonFe at Earths core conditions and show that the electronelectron scattering in epsilonFe exhibit a nearly perfect Fermiliquid (FL) behavior. Accordingly, the quadratic dependence of the scattering rate, typical of FLs, leads to a modification of the WiedemannFranz law and suppresses the thermal conductivity with respect to the electrical one. The consequence is a significant increase of the electronelectron thermal resistivity, which is found to be of comparable magnitude to the electronphonon one
Effect of pressure on phase stability in FeCr alloys by
A. V Ponomareva(
)
1 edition published in 2011 in English and held by 1 WorldCat member library worldwide
The effect of hydrostatic pressure on the phase stability of FeCr alloys has been studied using ab initio methods. We show that while pressure decreases the tendency toward the phase separation in the paramagnetic state of bcc alloys, in the ferromagnetic state it reduces the alloy stability at low Cr concentration and vice versa, makes the solid solution more stable at higher concentrations. This behavior of the phase stability can be predicted from the deviation of the lattice parameter from Vegards law in bcc FeCr alloys. On the atomic level, the pressure effect can be explained by the suppression of the local magnetic moments on Cr atoms, which gives rise to a decrease of the FeCr magnetic exchange interaction at the first coordination shell and, as a result, to the observed variation of the ordering tendency between the Fe and Cr atoms
1 edition published in 2011 in English and held by 1 WorldCat member library worldwide
The effect of hydrostatic pressure on the phase stability of FeCr alloys has been studied using ab initio methods. We show that while pressure decreases the tendency toward the phase separation in the paramagnetic state of bcc alloys, in the ferromagnetic state it reduces the alloy stability at low Cr concentration and vice versa, makes the solid solution more stable at higher concentrations. This behavior of the phase stability can be predicted from the deviation of the lattice parameter from Vegards law in bcc FeCr alloys. On the atomic level, the pressure effect can be explained by the suppression of the local magnetic moments on Cr atoms, which gives rise to a decrease of the FeCr magnetic exchange interaction at the first coordination shell and, as a result, to the observed variation of the ordering tendency between the Fe and Cr atoms
Theoretical prediction of properties of atomistic systems Density functional theory and machine learning by
Alexander Lindmaa(
)
1 edition published in 2017 in English and held by 1 WorldCat member library worldwide
The prediction of ground state properties of atomistic systems is of vital importance in technological advances as well as in the physical sciences. Fundamentally, these predictions are based on a quantummechanical description of manyelectron systems. One of the hitherto most prominent theories for the treatment of such systems is density functional theory (DFT). The main reason for its success is due to its balance of acceptable accuracy with computational efficiency. By now, DFT is applied routinely to compute the properties of atomic, molecular, and solid state systems. The general approach to solve the DFT equations is to use a densityfunctional approximation (DFA). In KohnSham (KS) DFT, DFAs are applied to the unknown exchangecorrelation (xc) energy. In orbitalfree DFT on the other hand, where the total energy is minimized directly with respect to the electron density, a DFA applied to the noninteracting kinetic energy is also required. Unfortunately, central DFAs in DFT fail to qualitatively capture many important aspects of electronic systems. Two prime examples are the description of localized electrons, and the description of systems where electronic edges are present. In this thesis, I use a model system approach to construct a DFA for the electron localization function (ELF). The very same approach is also taken to study the noninteracting kinetic energy density (KED) in the slowly varying limit of inhomogeneous electron densities, where the effect of electronic edges are effectively included. Apart from the work on model systems, extensions of an exchange energy functional with an improved KS orbital description are presented: a scheme for improving its description of energetics of solids, and a comparison of its description of an essential exact exchange feature known as the derivative discontinuity with numerical data for exact exchange. An emerging alternative route towards the prediction of the properties of atomistic systems is machine learning (ML). I present a number of ML methods for the prediction of solid formation energies, with an accuracy that is on par with KS DFT calculations, and with ordersofmagnitude lower computational cost
1 edition published in 2017 in English and held by 1 WorldCat member library worldwide
The prediction of ground state properties of atomistic systems is of vital importance in technological advances as well as in the physical sciences. Fundamentally, these predictions are based on a quantummechanical description of manyelectron systems. One of the hitherto most prominent theories for the treatment of such systems is density functional theory (DFT). The main reason for its success is due to its balance of acceptable accuracy with computational efficiency. By now, DFT is applied routinely to compute the properties of atomic, molecular, and solid state systems. The general approach to solve the DFT equations is to use a densityfunctional approximation (DFA). In KohnSham (KS) DFT, DFAs are applied to the unknown exchangecorrelation (xc) energy. In orbitalfree DFT on the other hand, where the total energy is minimized directly with respect to the electron density, a DFA applied to the noninteracting kinetic energy is also required. Unfortunately, central DFAs in DFT fail to qualitatively capture many important aspects of electronic systems. Two prime examples are the description of localized electrons, and the description of systems where electronic edges are present. In this thesis, I use a model system approach to construct a DFA for the electron localization function (ELF). The very same approach is also taken to study the noninteracting kinetic energy density (KED) in the slowly varying limit of inhomogeneous electron densities, where the effect of electronic edges are effectively included. Apart from the work on model systems, extensions of an exchange energy functional with an improved KS orbital description are presented: a scheme for improving its description of energetics of solids, and a comparison of its description of an essential exact exchange feature known as the derivative discontinuity with numerical data for exact exchange. An emerging alternative route towards the prediction of the properties of atomistic systems is machine learning (ML). I present a number of ML methods for the prediction of solid formation energies, with an accuracy that is on par with KS DFT calculations, and with ordersofmagnitude lower computational cost
Pressureinduced spinstate transition of iron in magnesiowustite (Fe, Mg)O by
I Leonov(
)
1 edition published in 2017 in English and held by 1 WorldCat member library worldwide
We present a detailed theoretical study of the electronic, magnetic, and structural properties of magnesiowustite Fe1 Mgx(x) O with x in the range between 0 and 0.875 using a fully charge selfconsistent implementation of the density functional theory plus dynamical meanfield theory method. In particular, we compute the electronic structure and phase stability of the rocksalt B1structured (Fe, Mg) O at high pressures relevant for the Earths lower mantle. We find that upon compression paramagnetic (Fe, Mg) O exhibits a spinstate transition of Fe2+ ions from a highspin to lowspin (HSLS) state which is accompanied by a collapse of local magnetic moments. The HSLS transition results in a substantial drop in the lattice volume by about 4%8%, implying a complex interplay between electronic and lattice degrees of freedom. Our results reveal a strong sensitivity of the calculated transition pressure Ptr. upon addition of Mg. While, for Ferich magnesiowustite with Mg x amp;lt; 0.5, Ptr. is about 80 GPa, for Mg x = 0.75 it drops to 52 GPa, i. e., by 35%. This behavior is accompanied by a substantial change in the spin transition range from 50 to 140 GPa in FeO to 30 to 90 GPa for x = 0.75. In addition, the calculated bulk modulus (in the HS state) is found to increase by similar to 12% from 142 GPa in FeO to 159 GPa in (Fe, Mg) O with Mg x = 0.875. We find that the pressureinduced HSLS transition has different consequences for the electronic properties of the Ferich and poor (Fe, Mg) O. For the Ferich (Fe, Mg) O, the transition is found to be accompanied by a Mott insulator to a (semi) metal phase transition. In contrast to that, for x amp;gt; 0.25, (Fe, Mg) O remains insulating up to the highest studied pressures, implying a Mottinsulator to bandinsulator phase transition at the HSLS transformation
1 edition published in 2017 in English and held by 1 WorldCat member library worldwide
We present a detailed theoretical study of the electronic, magnetic, and structural properties of magnesiowustite Fe1 Mgx(x) O with x in the range between 0 and 0.875 using a fully charge selfconsistent implementation of the density functional theory plus dynamical meanfield theory method. In particular, we compute the electronic structure and phase stability of the rocksalt B1structured (Fe, Mg) O at high pressures relevant for the Earths lower mantle. We find that upon compression paramagnetic (Fe, Mg) O exhibits a spinstate transition of Fe2+ ions from a highspin to lowspin (HSLS) state which is accompanied by a collapse of local magnetic moments. The HSLS transition results in a substantial drop in the lattice volume by about 4%8%, implying a complex interplay between electronic and lattice degrees of freedom. Our results reveal a strong sensitivity of the calculated transition pressure Ptr. upon addition of Mg. While, for Ferich magnesiowustite with Mg x amp;lt; 0.5, Ptr. is about 80 GPa, for Mg x = 0.75 it drops to 52 GPa, i. e., by 35%. This behavior is accompanied by a substantial change in the spin transition range from 50 to 140 GPa in FeO to 30 to 90 GPa for x = 0.75. In addition, the calculated bulk modulus (in the HS state) is found to increase by similar to 12% from 142 GPa in FeO to 159 GPa in (Fe, Mg) O with Mg x = 0.875. We find that the pressureinduced HSLS transition has different consequences for the electronic properties of the Ferich and poor (Fe, Mg) O. For the Ferich (Fe, Mg) O, the transition is found to be accompanied by a Mott insulator to a (semi) metal phase transition. In contrast to that, for x amp;gt; 0.25, (Fe, Mg) O remains insulating up to the highest studied pressures, implying a Mottinsulator to bandinsulator phase transition at the HSLS transformation
Magnetic nanoscale laminates with tunable exchange coupling from first principles by Martin Dahlqvist(
)
1 edition published in 2011 in English and held by 1 WorldCat member library worldwide
The M(n+1)AX(n) (MAX) phases are nanolaminated compounds with a unique combination of metallic and ceramic properties, not yet including magnetism. We carry out a systematic theoretical study of potential magnetic MAX phases and predict the existence of stable magnetic (Cr(1x)Mn(x))(2)AlC alloys. We show that in this system ferromagnetically ordered Mn layers are exchange coupled via nearly nonmagnetic Cr layers, forming an inherent structure of atomicthin magnetic multilayers, and that the degree of disorder between Cr and Mn in the alloy can be used to tune the sign and magnitude of the coupling
1 edition published in 2011 in English and held by 1 WorldCat member library worldwide
The M(n+1)AX(n) (MAX) phases are nanolaminated compounds with a unique combination of metallic and ceramic properties, not yet including magnetism. We carry out a systematic theoretical study of potential magnetic MAX phases and predict the existence of stable magnetic (Cr(1x)Mn(x))(2)AlC alloys. We show that in this system ferromagnetically ordered Mn layers are exchange coupled via nearly nonmagnetic Cr layers, forming an inherent structure of atomicthin magnetic multilayers, and that the degree of disorder between Cr and Mn in the alloy can be used to tune the sign and magnitude of the coupling
Temperature dependence of TiN elastic constants from ab initio molecular dynamics simulations by
Peter Steneteg(
)
1 edition published in 2013 in English and held by 1 WorldCat member library worldwide
Elastic properties of cubic TiN are studied theoretically in a wide temperature interval. Firstprinciples simulations are based on ab initio molecular dynamics (AIMD). Computational efficiency of the method is greatly enhanced by a careful preparation of the initial state of the simulation cell that minimizes or completely removes a need for equilibration and therefore allows for parallel AIMD calculations. Elastic constants C 11, C 12, and C 44 are calculated. A strong dependence on the temperature is predicted, with C 11 decreasing by more than 29% at 1800 K as compared to its value obtained at T=0 K. Furthermore, we analyze the effect of temperature on the elastic properties of polycrystalline TiN in terms of the bulk and shear moduli, the Young's modulus and Poisson ratio. We construct sound velocity anisotropy maps, investigate the temperature dependence of elastic anisotropy of TiN, and observe that the material becomes substantially more isotropic at high temperatures. Our results unambiguously demonstrate the importance of taking into account finite temperature effects in theoretical calculations of elastic properties of materials intended for hightemperature applications
1 edition published in 2013 in English and held by 1 WorldCat member library worldwide
Elastic properties of cubic TiN are studied theoretically in a wide temperature interval. Firstprinciples simulations are based on ab initio molecular dynamics (AIMD). Computational efficiency of the method is greatly enhanced by a careful preparation of the initial state of the simulation cell that minimizes or completely removes a need for equilibration and therefore allows for parallel AIMD calculations. Elastic constants C 11, C 12, and C 44 are calculated. A strong dependence on the temperature is predicted, with C 11 decreasing by more than 29% at 1800 K as compared to its value obtained at T=0 K. Furthermore, we analyze the effect of temperature on the elastic properties of polycrystalline TiN in terms of the bulk and shear moduli, the Young's modulus and Poisson ratio. We construct sound velocity anisotropy maps, investigate the temperature dependence of elastic anisotropy of TiN, and observe that the material becomes substantially more isotropic at high temperatures. Our results unambiguously demonstrate the importance of taking into account finite temperature effects in theoretical calculations of elastic properties of materials intended for hightemperature applications
Effect of Re content on elastic properties of B2 NiAl from ab initio calculations by
A. V Ponomareva(
)
1 edition published in 2014 in English and held by 1 WorldCat member library worldwide
The effect of substitutional alloying of Re on elastic properties of B2 NiAl has been studied using firstprinciples electronicstructure calculations by the exact muffintin orbitals method and the coherent potential approximation. Our calculations have shown that elastic constants C12, C44 and bulk modulus B of (Ni1xRex) Al alloys increase with Re composition almost linearly, but concentration dependence of elastic constants C11, Young modulus E, shear modulus G, G/B ratio and the Cauchy pressure PC is strongly nonmonotonously and has peculiarities near the concentration x = 30 at.% Re. Analyzing the density of states and Fermi surface sections we have a direct connection between the behavior of the elastic constants of (Ni1xRex) Al alloys and changes in the interatomic bonding and Fermi surface topology
1 edition published in 2014 in English and held by 1 WorldCat member library worldwide
The effect of substitutional alloying of Re on elastic properties of B2 NiAl has been studied using firstprinciples electronicstructure calculations by the exact muffintin orbitals method and the coherent potential approximation. Our calculations have shown that elastic constants C12, C44 and bulk modulus B of (Ni1xRex) Al alloys increase with Re composition almost linearly, but concentration dependence of elastic constants C11, Young modulus E, shear modulus G, G/B ratio and the Cauchy pressure PC is strongly nonmonotonously and has peculiarities near the concentration x = 30 at.% Re. Analyzing the density of states and Fermi surface sections we have a direct connection between the behavior of the elastic constants of (Ni1xRex) Al alloys and changes in the interatomic bonding and Fermi surface topology
Emergence of quantum critical charge and spinstate fluctuations near the pressureinduced Mott transition in MnO, FeO, CoO,
and NiO by
I Leonov(
)
1 edition published in 2020 in English and held by 1 WorldCat member library worldwide
We perform a comprehensive theoretical study of the pressureinduced evolution of the electronic structure, magnetic state, and phase stability of the late transition metal monoxides MnO, FeO, CoO, and NiO using a fully charge selfconsistent DFTPdynamical meanfield theory method. Our results reveal that the pressureinduced Mott insulatortometal phase transition in MnONiO is accompanied by a simultaneous collapse of local magnetic moments and lattice volume, implying a complex interplay between chemical bonding and electronic correlations. We compute the pressureinduced evolution of relative weights of the different valence states and spinstate configurations. Employing the concept of fluctuating valence in a correlated solid, we demonstrate that in MnO, FeO, and CoO a Mott insulatormetal transition and collapse of the local moments is accompanied by a sharp crossover of the spinstate and valence configurations. Our microscopic explanation of the magnetic collapse differs from the accepted picture and points out a remarkable dynamical coexistence (frustration) of the high, intermediate, and lowspin states. In particular, in MnO, the magnetic collapse is found to be driven by the appearance of the intermediatespin state (IS), competing with the lowspin (LS) state; in FeO, we observe a conventional highspin to lowspin (HSLS) crossover. Most interestingly, in CoO, we obtain a remarkable (dynamical) coexistence of the HS and LS states, i.e., a HSLS frustration, up to high pressure. Our results demonstrate the importance of quantum fluctuations of the valence and spin states for the understanding of quantum criticality of the Mott transitions
1 edition published in 2020 in English and held by 1 WorldCat member library worldwide
We perform a comprehensive theoretical study of the pressureinduced evolution of the electronic structure, magnetic state, and phase stability of the late transition metal monoxides MnO, FeO, CoO, and NiO using a fully charge selfconsistent DFTPdynamical meanfield theory method. Our results reveal that the pressureinduced Mott insulatortometal phase transition in MnONiO is accompanied by a simultaneous collapse of local magnetic moments and lattice volume, implying a complex interplay between chemical bonding and electronic correlations. We compute the pressureinduced evolution of relative weights of the different valence states and spinstate configurations. Employing the concept of fluctuating valence in a correlated solid, we demonstrate that in MnO, FeO, and CoO a Mott insulatormetal transition and collapse of the local moments is accompanied by a sharp crossover of the spinstate and valence configurations. Our microscopic explanation of the magnetic collapse differs from the accepted picture and points out a remarkable dynamical coexistence (frustration) of the high, intermediate, and lowspin states. In particular, in MnO, the magnetic collapse is found to be driven by the appearance of the intermediatespin state (IS), competing with the lowspin (LS) state; in FeO, we observe a conventional highspin to lowspin (HSLS) crossover. Most interestingly, in CoO, we obtain a remarkable (dynamical) coexistence of the HS and LS states, i.e., a HSLS frustration, up to high pressure. Our results demonstrate the importance of quantum fluctuations of the valence and spin states for the understanding of quantum criticality of the Mott transitions
Identification of Sivacancy related roomtemperature qubits in 4H silicon carbide by
Viktor Ivády(
)
1 edition published in 2017 in English and held by 1 WorldCat member library worldwide
The identification of a microscopic configuration of point defects acting as quantum bits is a key step in the advance of quantum information processing and sensing. Among the numerous candidates, siliconvacancy related centers in silicon carbide (SiC) have shown remarkable properties owing to their particular spin3/2 ground and excited states. Although, these centers were observed decades ago, two competing models, the isolated negatively charged silicon vacancy and the complex of negatively charged silicon vacancy and neutral carbon vacancy [Phys. Rev. Lett. 115, 247602 (2015)], are still argued as an origin. By means of highprecision firstprinciples calculations and highresolution electron spin resonance measurements, we here unambiguously identify the Sivacancy related qubits in hexagonal SiC as isolated negatively charged silicon vacancies. Moreover, we identify the Sivacancy qubit configurations that provide roomtemperature optical readout
1 edition published in 2017 in English and held by 1 WorldCat member library worldwide
The identification of a microscopic configuration of point defects acting as quantum bits is a key step in the advance of quantum information processing and sensing. Among the numerous candidates, siliconvacancy related centers in silicon carbide (SiC) have shown remarkable properties owing to their particular spin3/2 ground and excited states. Although, these centers were observed decades ago, two competing models, the isolated negatively charged silicon vacancy and the complex of negatively charged silicon vacancy and neutral carbon vacancy [Phys. Rev. Lett. 115, 247602 (2015)], are still argued as an origin. By means of highprecision firstprinciples calculations and highresolution electron spin resonance measurements, we here unambiguously identify the Sivacancy related qubits in hexagonal SiC as isolated negatively charged silicon vacancies. Moreover, we identify the Sivacancy qubit configurations that provide roomtemperature optical readout
Ab initio calculation of the solution enthalpies of substitutional and interstitial impurities in paramagnetic fcc Fe by
A. V Ponomareva(
)
1 edition published in 2014 in English and held by 1 WorldCat member library worldwide
In the framework of disordered local moment approach by using magnetic sampling method, we suggested a model that takes into account the magnetic disorder in paramagnetic Fe with point defects. We calculate solution enthalpies of substitutional (Nb, V) and interstitial (C, N) impurities in paramagnetic facecentered cubic Fe and obtain results that are in agreement with available experimental data. It is found that both interstitial and substitutional atoms may favor the local magnetic polarization of the Fe host around the impurities by decreasing the potential energy of the system. The possibility of a formation of predominantly ferromagnetic Fe clusters around carbon in the temperature range of overcooled austenite is discussed
1 edition published in 2014 in English and held by 1 WorldCat member library worldwide
In the framework of disordered local moment approach by using magnetic sampling method, we suggested a model that takes into account the magnetic disorder in paramagnetic Fe with point defects. We calculate solution enthalpies of substitutional (Nb, V) and interstitial (C, N) impurities in paramagnetic facecentered cubic Fe and obtain results that are in agreement with available experimental data. It is found that both interstitial and substitutional atoms may favor the local magnetic polarization of the Fe host around the impurities by decreasing the potential energy of the system. The possibility of a formation of predominantly ferromagnetic Fe clusters around carbon in the temperature range of overcooled austenite is discussed
HighPressure Synthesis of MetalInorganic Frameworks Hf4N20 center dot N2, WN8 center dot N2, and Os5N28 center dot 3 N2
with Polymeric Nitrogen Linkers by
Maxim Bykov(
)
1 edition published in 2020 in English and held by 1 WorldCat member library worldwide
Polynitrides are intrinsically thermodynamically unstable at ambient conditions and require peculiar synthetic approaches. Now, a onestep synthesis of metalinorganic frameworks Hf4N20 center dot N2, WN 8 center dot N2, and Os5N28 center dot 3N2 via direct reactions between elements in a diamond anvil cell at pressures exceeding 100 GPa is reported. The porous frameworks (Hf4N20, WN 8, and Os5N28) are built from transitionmetal atoms linked either by polymeric polydiazenediyl (polyacetylenelike) nitrogen chains or through dinitrogen units. Triply bound dinitrogen molecules occupy channels of these frameworks. Owing to conjugated polydiazenediyl chains, these compounds exhibit metallic properties. The highpressure reaction between Hf and N2 also leads to a noncentrosymmetric polynitride Hf2N11 that features doublehelix catenapoly[tetraz1ene1,4diyl] nitrogen chains [NNN=N](infinity.)
1 edition published in 2020 in English and held by 1 WorldCat member library worldwide
Polynitrides are intrinsically thermodynamically unstable at ambient conditions and require peculiar synthetic approaches. Now, a onestep synthesis of metalinorganic frameworks Hf4N20 center dot N2, WN 8 center dot N2, and Os5N28 center dot 3N2 via direct reactions between elements in a diamond anvil cell at pressures exceeding 100 GPa is reported. The porous frameworks (Hf4N20, WN 8, and Os5N28) are built from transitionmetal atoms linked either by polymeric polydiazenediyl (polyacetylenelike) nitrogen chains or through dinitrogen units. Triply bound dinitrogen molecules occupy channels of these frameworks. Owing to conjugated polydiazenediyl chains, these compounds exhibit metallic properties. The highpressure reaction between Hf and N2 also leads to a noncentrosymmetric polynitride Hf2N11 that features doublehelix catenapoly[tetraz1ene1,4diyl] nitrogen chains [NNN=N](infinity.)
Correlation strength, orbitalselective incoherence, and local moments formation in the magnetic MAXphase Mn2GaC by H. J. M Jonsson(
)
1 edition published in 2022 in English and held by 1 WorldCat member library worldwide
We perform a theoretical study of the electronic structure and magnetic properties of the prototypical magnetic MAXphase Mn2GaC with the main focus given to the origin of magnetic interactions in this system. Using the density functional theory+dynamical meanfield theory (DFT+DMFT) method, we explore the effects of electronelectron interactions and magnetic correlations on the electronic properties, magnetic state, and spectral weight coherence of paramagnetic and magnetically ordered phases of Mn2GaC. We also benchmark the DFTbased disordered local moment approach for this system by comparing the obtained electronic and magnetic properties with that of the DFT+DMFT method. Our results reveal a complex magnetic behavior characterized by a near degeneracy of the ferroand antiferromagnetic configurations of Mn2GaC, implying a high sensitivity of its magnetic state to fine details of the crystal structure and unitcell volume, consistent with experimental observations. We observe robust localmoment behavior and orbitalselective incoherence of the spectral properties of Mn2GaC, implying the importance of orbitaldependent localization of the Mn 3d states. We find that Mn2GaC can be described in terms of local magnetic moments, which may be modeled by DFT with disordered local moments. However, the magnetic properties are dictated by the proximity to the regime of formation of local magnetic moments, in which the localization is in fact driven by Hunds exchange interaction, and not the Coulomb interaction
1 edition published in 2022 in English and held by 1 WorldCat member library worldwide
We perform a theoretical study of the electronic structure and magnetic properties of the prototypical magnetic MAXphase Mn2GaC with the main focus given to the origin of magnetic interactions in this system. Using the density functional theory+dynamical meanfield theory (DFT+DMFT) method, we explore the effects of electronelectron interactions and magnetic correlations on the electronic properties, magnetic state, and spectral weight coherence of paramagnetic and magnetically ordered phases of Mn2GaC. We also benchmark the DFTbased disordered local moment approach for this system by comparing the obtained electronic and magnetic properties with that of the DFT+DMFT method. Our results reveal a complex magnetic behavior characterized by a near degeneracy of the ferroand antiferromagnetic configurations of Mn2GaC, implying a high sensitivity of its magnetic state to fine details of the crystal structure and unitcell volume, consistent with experimental observations. We observe robust localmoment behavior and orbitalselective incoherence of the spectral properties of Mn2GaC, implying the importance of orbitaldependent localization of the Mn 3d states. We find that Mn2GaC can be described in terms of local magnetic moments, which may be modeled by DFT with disordered local moments. However, the magnetic properties are dictated by the proximity to the regime of formation of local magnetic moments, in which the localization is in fact driven by Hunds exchange interaction, and not the Coulomb interaction
Metastable silica high pressure polymorphs as structural proxies of deep Earth silicate melts by
E Bykova(
)
1 edition published in 2018 in English and held by 1 WorldCat member library worldwide
Modelling of processes involving deep Earth liquids requires information on their structures and compression mechanisms. However, knowledge of the local structures of silicates and silica (SiO2) melts at deep mantle conditions and of their densification mechanisms is still limited. Here we report the synthesis and characterization of metastable highpressure silica phases, coesiteIV and coesiteV, using in situ singlecrystal Xray diffraction and ab initio simulations. Their crystal structures are drastically different from any previously considered models, but explain well features of pairdistribution functions of highly densified silica glass and molten basalt at high pressure. Built of four, five, and sixcoordinated silicon, coesiteIV and coesiteV contain SiO6 octahedra, which, at odds with 3rd Paulings rule, are connected through common faces. Our results suggest that possible silicate liquids in Earths lower mantle may have complex structures making them more compressible than previously supposed
1 edition published in 2018 in English and held by 1 WorldCat member library worldwide
Modelling of processes involving deep Earth liquids requires information on their structures and compression mechanisms. However, knowledge of the local structures of silicates and silica (SiO2) melts at deep mantle conditions and of their densification mechanisms is still limited. Here we report the synthesis and characterization of metastable highpressure silica phases, coesiteIV and coesiteV, using in situ singlecrystal Xray diffraction and ab initio simulations. Their crystal structures are drastically different from any previously considered models, but explain well features of pairdistribution functions of highly densified silica glass and molten basalt at high pressure. Built of four, five, and sixcoordinated silicon, coesiteIV and coesiteV contain SiO6 octahedra, which, at odds with 3rd Paulings rule, are connected through common faces. Our results suggest that possible silicate liquids in Earths lower mantle may have complex structures making them more compressible than previously supposed
Vibrational free energy and phase stability of paramagnetic and antiferromagnetic CrN from ab initio molecular dynamics by Nina Shulumba(
)
1 edition published in 2014 in English and held by 1 WorldCat member library worldwide
We present a theoretical firstprinciples method to calculate the free energy of a magnetic system in its hightemperature paramagnetic phase, including vibrational, electronic, and magnetic contributions. The method for calculating free energies is based on ab initio molecular dynamics and combines a treatment of disordered magnetism using disordered local moments molecular dynamics with the temperaturedependent effective potential method to obtain the vibrational contribution to the free energy. We illustrate the applicability of the method by obtaining the anharmonic free energy for the paramagnetic cubic and the antiferromagnetic orthorhombic phases of chromium nitride. The influence of lattice dynamics on the transition between the two phases is demonstrated by constructing the temperaturepressure phase diagram
1 edition published in 2014 in English and held by 1 WorldCat member library worldwide
We present a theoretical firstprinciples method to calculate the free energy of a magnetic system in its hightemperature paramagnetic phase, including vibrational, electronic, and magnetic contributions. The method for calculating free energies is based on ab initio molecular dynamics and combines a treatment of disordered magnetism using disordered local moments molecular dynamics with the temperaturedependent effective potential method to obtain the vibrational contribution to the free energy. We illustrate the applicability of the method by obtaining the anharmonic free energy for the paramagnetic cubic and the antiferromagnetic orthorhombic phases of chromium nitride. The influence of lattice dynamics on the transition between the two phases is demonstrated by constructing the temperaturepressure phase diagram
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 Linköpings universitet Tekniska högskolan Publisher
 Linköpings universitet Institutionen för fysik, kemi och biologi Publisher
 Alling, Björn Author
 Tasnadi, Ferenc Author
 Simak, Sergey
 Hultman, Lars
 Ponomareva, A. V. Author
 Ivády, Viktor Author
 Odén, Magnus
 Marten, Tobias Author
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