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BETA
Simak, Sergei I
Alternative names
Publications (10 of 76) Show all publications
Kerdsongpanya, S., Hellman, O., Sun, B., Kan Koh, Y., Lu, J., Van Nong, N., . . . Eklund, P. (2017). Phonon thermal conductivity of scandium nitride for thermoelectrics from first-principles calculations and thin-film growth. Physical Review B, 96(19), Article ID 195417.
Open this publication in new window or tab >>Phonon thermal conductivity of scandium nitride for thermoelectrics from first-principles calculations and thin-film growth
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2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 19, article id 195417Article in journal (Refereed) Published
Abstract [en]

The knowledge of lattice thermal conductivity of materials under realistic conditions is vitally important since many modern technologies require either high or low thermal conductivity. Here, we propose a theoretical model for determining lattice thermal conductivity, which takes into account the effect of microstructure. It is based on ab initio description that includes the temperature dependence of the interatomic force constants and treats anharmonic lattice vibrations. We choose ScN as a model system, comparing the computational predictions to the experimental data by time-domain thermoreflectance. Our experimental results show a trend of reduction in lattice thermal conductivity with decreasing domain size predicted by the theoretical model. These results suggest a possibility to control thermal conductivity by microstructural tailoring and provide a predictive tool for the effect of the microstructure on the lattice thermal conductivity of materials based on ab initio calculations.

Place, publisher, year, edition, pages
American Physical Society, 2017
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-143238 (URN)10.1103/PhysRevB.96.195417 (DOI)000414738200008 ()
Note

Funding Agencies|European Research Council under the European Communitys Seventh Framework Programme [FP/2007-2013]; ERC [335383]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Swedish Research Council [2012-4430, 2016-03365, 330-2014-6336, 2014-4750, 637-2013-7296]; Linnaeus Environment LiLi-NFM; Swedish Foundation for Strategic Research (SSF) through the Future Research Leaders 5 Program; NanoCaTe project (FP7) [604647]; National University of Singapore Startup Grant

Available from: 2017-11-27 Created: 2017-11-27 Last updated: 2017-12-05Bibliographically approved
Wang, F., Abrikosov, I., Simak, S., Odén, M., Muecklich, F. & Tasnadi, F. (2016). Coherency effects on the mixing thermodynamics of cubic Ti1-xAlxN/TiN(001) multilayers. PHYSICAL REVIEW B, 93(17), 174201
Open this publication in new window or tab >>Coherency effects on the mixing thermodynamics of cubic Ti1-xAlxN/TiN(001) multilayers
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2016 (English)In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 17, p. 174201-Article in journal (Refereed) Published
Abstract [en]

In this work, we discuss the mixing thermodynamics of cubic (B1) Ti1-xAlxN/TiN(001) multilayers. We show that interfacial effects suppress the mixing enthalpy compared to bulk Ti1-xAlxN. The strongest stabilization occurs for compositions in which the mixing enthalpy of bulk Ti1-xAlxN has its maximum. The effect is split into a strain and an interfacial (or chemical) contribution, and we show that both contributions are significant. An analysis of the local atomic structure reveals that the Ti atoms located in the interfacial layers relax significantly different from those in the other atomic layers of the multilayer. Considering the electronic structure of the studied system, we demonstrate that the lower Ti-site projected density of states at epsilon(F) in the Ti1-xAlxN/TiN multilayers compared to the corresponding monolithic bulk explains a decreased tendency toward decomposition.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2016
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-129166 (URN)10.1103/PhysRevB.93.174201 (DOI)000375990200003 ()
Note

Funding Agencies|Swedish Foundation for Strategic Research (SSF) project SRL [10-0026]; Erasmus Mundus Joint European Doctoral Programme DocMASE; Multiscale computational-design of novel hard nanostructure coatings; Swedish Research Council (VR) [2015-04391, 621-2012-4401, 2014-4750]; Grant of Ministry of Education and Science of the Russian Federation [14.Y26.31.0005]; Tomsk State University Academic D. I. Mendeleev Fund Program [8.1.18.2015]; LiLi-NFM; Swedish Government Strategic Research Area Grant in Materials Science

Available from: 2016-06-13 Created: 2016-06-13 Last updated: 2018-02-09
Ektarawong, A., Simak, S., Hultman, L., Birch, J., Tasnádi, F., Wang, F. & Alling, B. (2016). Effects of configurational disorder on the elastic properties of icosahedral boron-rich alloys based on B6O, B13C2, and B4C, and their mixing thermodynamics. Journal of Chemical Physics, 144(13), Article ID 134503.
Open this publication in new window or tab >>Effects of configurational disorder on the elastic properties of icosahedral boron-rich alloys based on B6O, B13C2, and B4C, and their mixing thermodynamics
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2016 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 144, no 13, article id 134503Article in journal (Refereed) Published
Abstract [en]

The elastic properties of alloys between boron suboxide (B6O) and boron carbide (B13C2), denoted by (B6O)1−x(B13C2)x, as well as boron carbide with variable carbon content, ranging from B13C2 to B4C are calculated from first-principles. Furthermore, the mixing thermodynamics of (B6O)1−x(B13C2)x is studied. A superatom-special quasirandom structure approach is used for modeling different atomic configurations, in which effects of configurational disorder between the carbide and suboxide structural units, as well as between boron and carbon atoms within the units, are taken into account. Elastic properties calculations demonstrate that configurational  disorder in B13C2, where a part of the C atoms in the CBC chains substitute for B atoms in the B12 icosahedra, drastically increase the Young’s and shear modulus, as compared to an atomically ordered state, B12(CBC). These calculated elastic moduli of the disordered state are in excellent agreement with experiments. Configurational disorder between boron and carbon can also explain the experimentally observed almost constant elastic moduli of boron carbide as the carbon content is changed from B4C to B13C2. The elastic moduli of the (B6O)1−x(B13C2)x system are also practically unchanged with composition if boron-carbon disorder is taken into account. By investigating the mixing thermodynamics of the alloys, in which the Gibbs free energy is determined within the mean-field approximation for the configurational entropy, we outline the pseudo-binary phase diagram of (B6O)1−x(B13C2)x. The phase diagram reveals the existence of a miscibility gap at all temperatures up to the melting point. Also, the coexistence of B6O-rich as well as ordered or disordered B13C2-rich domains in the material prepared through equilibrium routes is predicted.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2016
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-122425 (URN)10.1063/1.4944982 (DOI)000374527900023 ()27059576 (PubMedID)
Note

Funding agencies:Swedish Research Council (VR) [621-2011-4417, 330-2014-6336, 2011-42-59]; CeNano at Linkoping University; Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST "MISiS" [K3-2014-049]; LiLi-

At the time for thesis presentation publication was in status: Manuscript

Available from: 2015-11-02 Created: 2015-11-02 Last updated: 2017-12-01Bibliographically approved
Nilsson, J. O., Yu Vekilova, O., Hellman, O., Klarbring, J., Simak, S. & Skorodumova, N. V. (2016). Ionic conductivity in Gd-doped CeO2: Ab initio color-diffusion nonequilibrium molecular dynamics study. Physical Review B, 93(2), 024102
Open this publication in new window or tab >>Ionic conductivity in Gd-doped CeO2: Ab initio color-diffusion nonequilibrium molecular dynamics study
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2016 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 93, no 2, p. 024102-Article in journal (Refereed) Published
Abstract [en]

A first-principles nonequilibrium molecular dynamics (NEMD) study employing the color-diffusion algorithm has been conducted to obtain the bulk ionic conductivity and the diffusion constant of gadolinium-doped cerium oxide (GDC) in the 850-1150 K temperature range. Being a slow process, ionic diffusion in solids usually requires simulation times that are prohibitively long for ab initio equilibrium molecular dynamics. The use of the color-diffusion algorithm allowed us to substantially speed up the oxygen-ion diffusion. The key parameters of the method, such as field direction and strength as well as color-charge distribution, have been investigated and their optimized values for the considered system have been determined. The calculated ionic conductivity and diffusion constants are in good agreement with available experimental data.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2016
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-124465 (URN)10.1103/PhysRevB.93.024102 (DOI)000367662100002 ()
Note

Funding Agencies|Swedish Energy Agency (STEM) [355151]; Carl Tryggers Foundation [CTS 14:433]; Swedish Research Council (VR) [2014-5993, 2014-4750, 637-2013-7296]; LiLi-NFM; Swedish Government Strategic Research Area Grant in Materials Science

Available from: 2016-02-02 Created: 2016-02-01 Last updated: 2017-11-30
Ektarawong, A., Simak, S., Hultman, L., Birch, J. & Alling, B. (2015). Configurational order-disorder induced metal-nonmetal transition in B13C2 studied with first-principles superatom-special quasirandom structure method. Physical Review B. Condensed Matter and Materials Physics, 92(1), Article ID 014202.
Open this publication in new window or tab >>Configurational order-disorder induced metal-nonmetal transition in B13C2 studied with first-principles superatom-special quasirandom structure method
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2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 1, article id 014202Article in journal (Refereed) Published
Abstract [en]

Due to a large discrepancy between theory and experiment, the electronic character of crystalline boron carbide B13C2 has been a controversial topic in the field of icosahedral boron-rich solids. We demonstrate that this discrepancy is removed when configurational disorder is accurately considered in the theoretical calculations. We find that while the ordered ground state B13C2 is metallic, the configurationally disordered B13C2, modeled with a superatom-special quasirandom structure method, goes through a metal to nonmetal transition as the degree of disorder is increased with increasing temperature. Specifically, one of the chain-end carbon atoms in the CBC chains substitutes a neighboring equatorial boron atom in a B-12 icosahedron bonded to it, giving rise to a B11Ce(BBC) unit. The atomic configuration of the substitutionally disordered B13C2 thus tends to be dominated by a mixture between B-12(CBC) and B11Ce(BBC). Due to splitting of valence states in B11Ce(BBC), the electron deficiency in B-12(CBC) is gradually compensated.

Place, publisher, year, edition, pages
American Physical Society, 2015
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-120344 (URN)10.1103/PhysRevB.92.014202 (DOI)000357484100001 ()
Note

Funding Agencies|Swedish Research Council (VR) [621-2011-4417, 330-2014-6336, 2014-4750]; CeNano at Linkoping University; LiLi-NFM; Swedish Government Strategic Research Area Grant in Materials Science

Available from: 2015-07-31 Created: 2015-07-31 Last updated: 2017-12-04
Vekilova, O., Pourovskii, L. V., Abrikosov, I. & Simak, S. (2015). Electronic correlations in Fe at Earths inner core conditions: Effects of alloying with Ni. Physical Review B. Condensed Matter and Materials Physics, 91(24), 245116
Open this publication in new window or tab >>Electronic correlations in Fe at Earths inner core conditions: Effects of alloying with Ni
2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, no 24, p. 245116-Article in journal (Refereed) Published
Abstract [en]

We have studied the body-centered cubic (bcc), face-centered cubic (fcc), and hexagonal close-packed (hcp) phases of Fe alloyed with 25 at.% of Ni at Earths core conditions using an ab initio local density approximation + dynamical mean-field theory approach. The alloys have been modeled by ordered crystal structures based on the bcc, fcc, and hcp unit cells with the minimum possible cell size allowing for the proper composition. Our calculations demonstrate that the strength of electronic correlations on the Fe 3d shell is highly sensitive to the phase and local environment. In the bcc phase, the 3d electrons at the Fe site with Fe only nearest neighbors remain rather strongly correlated, even at extreme pressure-temperature conditions, with the local and uniform magnetic susceptibility exhibiting a Curie-Weiss-like temperature evolution and the quasiparticle lifetime Gamma featuring a non-Fermi-liquid temperature dependence. In contrast, for the corresponding Fe site in the hcp phase, we predict a weakly correlated Fermi-liquid state with a temperature-independent local susceptibility and a quadratic temperature dependence of Gamma. The iron sites with nickel atoms in the local environment exhibit behavior in the range between those two extreme cases, with the strength of correlations gradually increasing along the hcp-fcc-bcc sequence. Further, the intersite magnetic interactions in the bcc and hcp phases are also strongly affected by the presence of Ni nearest neighbors. The sensitivity to the local environment is related to modifications of the Fe partial density of states due to mixing with Ni 3d states.

Place, publisher, year, edition, pages
American Physical Society, 2015
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-119789 (URN)10.1103/PhysRevB.91.245116 (DOI)000355721300007 ()
Note

Funding Agencies|HPC-Europa2; Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST "MISiS" [K3-2015-038]; PHD DALEN [26228RM]; Swedish Research Council (VR) [621-2011-4426, 2011-42-59, 2014-4750]; Linkoping Linnaeus Initiative for Novel Functional Materials (LiLi-NFM); Swedish Foundation for Strategic Research (SSF) program [SRL10-0026]; Swedish Government Strategic Research Area Grant in Materials Science "Advanced Functional Materials" (AFM); Swedish e-Science Research Centre (SeRC); Ministry of Education and Science of the Russian Federation [14.Y26.31.0005]

Available from: 2015-06-26 Created: 2015-06-26 Last updated: 2017-12-04
Lukinov, T., Simak, S. & Belonoshko, A. B. (2015). Sound velocity in shock compressed molybdenum obtained by ab initio molecular dynamics. Physical Review B. Condensed Matter and Materials Physics, 92(6), 060101
Open this publication in new window or tab >>Sound velocity in shock compressed molybdenum obtained by ab initio molecular dynamics
2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 6, p. 060101-Article in journal (Refereed) Published
Abstract [en]

The sound velocity of Mo along the Hugoniot adiabat is calculated from first principles using density-functional theory based molecular dynamics. These data are compared to the sound velocity as measured in recent experiments. The theoretical and experimental Hugoniot and sound velocities are in very good agreement up to pressures of 210 GPa and temperatures of 3700 K on the Hugoniot. However, above that point the experiment and theory diverge. This implies that Mo undergoes a phase transition at about the same point. Considering that the melting point of Mo is likely much higher at that pressure, the related change in the sound velocity in experiment can be ascribed to a solid-solid transition.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2015
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-122219 (URN)10.1103/PhysRevB.92.060101 (DOI)000362212200001 ()
Note

Funding Agencies|Swedish Research Council (VR) [2013-5767, 2014-4750]

Available from: 2015-10-26 Created: 2015-10-23 Last updated: 2017-12-01
Arapan, S., Simak, S. & Skorodumova, N. V. (2015). Volume-dependent electron localization in ceria. Physical Review B. Condensed Matter and Materials Physics, 91(12), 125108
Open this publication in new window or tab >>Volume-dependent electron localization in ceria
2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, no 12, p. 125108-Article in journal (Refereed) Published
Abstract [en]

We have performed a numerical study of the process of electron localization in reduced ceria. Our results show that different localized charge distributions can be attained in a bulk system by varying the lattice parameter. We demonstrate that the effect of electron localization is mainly determined by lattice relaxation and an accurate account for the effects of electronic correlation is necessary to achieve localized charge distribution.

Place, publisher, year, edition, pages
American Physical Society, 2015
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-116953 (URN)10.1103/PhysRevB.91.125108 (DOI)000350500100003 ()
Note

Funding Agencies|Swedish Research Council [2014-4750]; Swedish Energy Agency (STEM); Carl Tryggers Foundation; LiLi-NFM; Swedish Government Strategic Research Area Grant in Materials Science

Available from: 2015-04-13 Created: 2015-04-10 Last updated: 2017-12-04
Ektarawong, A., Simak, S., Hultman, L., Birch, J. & Alling, B. (2014). First-principles study of configurational disorder in B4C using a superatom-special quasirandom structure method. Paper presented at Conference name. Physical Review B. Condensed Matter and Materials Physics, 90(2), Article ID 024204.
Open this publication in new window or tab >>First-principles study of configurational disorder in B4C using a superatom-special quasirandom structure method
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2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 2, article id 024204Article in journal (Refereed) Published
Abstract [en]

Configurationally disordered crystalline boron carbide, with the composition B4C, is studied using first-principles calculations. We investigate both dilute and high concentrations of carbon-boron substitutional defects. For the latter purpose, we suggest a superatoms picture of the complex structure and combine it with a special quasirandom structure approach for disorder. In this way, we model a random distribution of high concentrations of the identified low-energy defects: (1) bipolar defects and (2) rotation of icosahedral carbon among the three polar-up sites. Additionally, the substitutional disorder of the icosahedral carbon at all six polar sites, as previously discussed in the literature, is also considered. Two configurational phase transitions from the ordered to the disordered configurations are predicted to take place upon an increase in temperature using a mean-field approximation for the entropy. The first transition, at 870 K, induces substitutional disorder of the icosahedral carbon atoms among the three polar-up sites; meanwhile the second transition, at 2325 K, reveals the random substitution of the icosahedral carbon atoms at all six polar sites coexisting with bipolar defects. Already the first transition removes the monoclinic distortion existing in the ordered ground-state configuration and restore the rhombohedral system (R3m). The restoration of inversion symmetry yielding the full rhombohedral symmetry (R (3) over barm) on average, corresponding to what is reported in the literature, is achieved after the second transition. Investigating the effects of high pressure on the configurational stability of the disordered B4C phases reveals a tendency to stabilize the ordered ground-state configuration as the configurationally ordering/disordering transition temperature increases with pressure exerted on B4C. The electronic density of states, obtained from the disordered phases, indicates a sensitivity of the band gap to the degree of configurational disorder in B4C.

Place, publisher, year, edition, pages
American Physical Society, 2014
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-109591 (URN)10.1103/PhysRevB.90.024204 (DOI)000339481700003 ()
Conference
Conference name
Available from: 2014-08-21 Created: 2014-08-21 Last updated: 2017-12-05
Pourovskii, L. V., Miyake, T., Simak, S., Ruban, A. V., Dubrovinsky, L. & Abrikosov, I. (2013). Electronic properties and magnetism of iron at the Earth's inner core conditions. Physical Review B. Condensed Matter and Materials Physics, 87(11)
Open this publication in new window or tab >>Electronic properties and magnetism of iron at the Earth's inner core conditions
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2013 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 11Article in journal (Refereed) Published
Abstract [en]

We employ state-of-the-art ab initio simulations within the dynamical mean-field theory to study three likely phases of iron (hcp, fcc, and bcc) at the Earth's core conditions. We demonstrate that the correction to the electronic free energy due to correlations can be significant for the relative stability of the phases. The strongest effect is observed in bcc Fe, which shows a non-Fermi-liquid behavior, and where a Curie-Weiss behavior of the uniform susceptibility hints at a local magnetic moment still existing at 5800 K and 300 GPa. We predict that all three structures have sufficiently high magnetic susceptibility to stabilize the geodynamo.

Place, publisher, year, edition, pages
American Physical Society, 2013
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-91012 (URN)10.1103/PhysRevB.87.115130 (DOI)000316414700004 ()
Note

Funding Agencies|Swedish e-science Research Centre (SeRC)||Swedish Research Centre for Advanced Functional Materials (AFM)||Linkoping Linnaeus Initiative for Novel Functional Materials (LiLI-NFM)||Swedish Foundation for Strategic Research (SSF)|10-0026|Swedish Research Council (VR)|621-2011-4426|PHD DALEN Project|26228RM|German Science Foundation (DFG)||German Ministry for Education and Research (BMBF)||

Available from: 2013-04-12 Created: 2013-04-11 Last updated: 2017-12-06Bibliographically approved
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