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Ehteshami, Hossein
Publications (5 of 5) Show all publications
Ehteshami, H. & Ruban, A. V. (2018). High-temperature thermophysical properties of gamma- and delta-Mn from first principles. PHYSICAL REVIEW MATERIALS, 2(3), Article ID 034405.
Open this publication in new window or tab >>High-temperature thermophysical properties of gamma- and delta-Mn from first principles
2018 (English)In: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 2, no 3, article id 034405Article in journal (Refereed) Published
Abstract [en]

Thermophysical properties of gamma-and delta-Mn phases have been investigated using first-principles calculations in their thermodynamically stable temperature range. An adiabatic approximation is used for partitioning of the Helmholtz free energy into electronic, magnetic, and vibrational contributions from the corresponding temperature induced excitations, where the fastest degree of freedom has been included in the slower ones. Namely, electronic excitations (on a one-electron level) have been included directly in the first-principles calculations at the corresponding temperatures. Magnetic excitations in the paramagnetic state then have been taken into consideration in the two opposite limits: localized, considering only transverse spin fluctuations (TSF), and itinerant, allowing for the full coupling of transverse and longitudinal spin fluctuations (LSF). Magnetic contribution to the free energy has been included in the calculations of the vibrational one, which has been obtained within the Debye-Gruneisen model. The calculated thermophysical properties such as lattice constance, thermal lattice expansion, and heat capacity are in good agreement with available experimental data, especially in the case when the itinerant magnetic model is chosen. We also present our results for elastic properties at high temperatures.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-228153 (URN)10.1103/PhysRevMaterials.2.034405 (DOI)000428785600002 ()2-s2.0-85059613698 (Scopus ID)
Note

QC 20180521

Available from: 2018-05-21 Created: 2018-05-21 Last updated: 2019-05-07Bibliographically approved
Yan, J.-Y., Ehteshami, H., Korzhavyi, P. . & Borgenstam, A. (2017). Sigma 3(111) grain boundary of body-centered cubic Ti-Mo and Ti-V alloys: First-principles and model calculations. PHYSICAL REVIEW MATERIALS, 1(2), Article ID 023602.
Open this publication in new window or tab >>Sigma 3(111) grain boundary of body-centered cubic Ti-Mo and Ti-V alloys: First-principles and model calculations
2017 (English)In: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 1, no 2, article id 023602Article in journal (Refereed) Published
Abstract [en]

The energetics and atomic structures of Sigma 3[1 (1) over bar0](111) grain boundary (GB) of body-centered cubic (bcc) Ti-Mo and Ti-V alloys are investigated using density-functional-theory calculations and virtual crystal approximation. The electron density in bcc structure and the atomic displacements and excess energy of the GB are correlated to bcc-omega phase stability. Model calculations based on pairwise interplanar interactions successfully reproduce thechemical part of GB energy. The chemical GB energy can be expressed as a sum of excess pairwise interactions between bcc (111) layers, which are obtained from Gaussian elimination of the total energies of a number of periodic structures. The energy associated with the relaxation near the GB is solved by numerical minimization using the derivatives of the excess interactions. Anharmonic interlayer interactions are necessary for obtaining accurate relaxation energy and excess GB volume from model calculations. The effect of GB on vibrational spectrum is also investigated. Segregation energies of B and Y to a substitutional site on the GB plane are calculated. Preliminary results suggest that Y tends to segregate, while B tends to antisegregate.

National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-220299 (URN)10.1103/PhysRevMaterials.1.023602 (DOI)000416555200005 ()2-s2.0-85053854667 (Scopus ID)
Note

QC 20171221

Available from: 2017-12-21 Created: 2017-12-21 Last updated: 2019-03-19Bibliographically approved
Ehteshami, H. & Korzhavyi, P. . (2017). Thermophysical properties of paramagnetic Fe from first principles. Physical Review B, 96(22), Article ID 224406.
Open this publication in new window or tab >>Thermophysical properties of paramagnetic Fe from first principles
2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 22, article id 224406Article in journal (Refereed) Published
Abstract [en]

A computationally efficient, yet general, free-energy modeling scheme is developed based on first-principles calculations. Finite-temperature disorder associated with the fast (electronic and magnetic) degrees of freedom is directly included in the electronic structure calculations, whereas the vibrational free energy is evaluated by a proposed model that uses elastic constants to calculate average sound velocity of the quasiharmonic Debye model. The proposed scheme is tested by calculating the lattice parameter, heat capacity, and single-crystal elastic constants of alpha-, gamma-, and delta-iron as functions of temperature in the range 1000-1800 K. The calculations accurately reproduce the well-established experimental data on thermal expansion and heat capacity of gamma- and delta-iron. Electronic and magnetic excitations are shown to account for about 20% of the heat capacity for the two phases. Nonphonon contributions to thermal expansion are 12% and 10% for alpha- and delta-Fe and about 30% for gamma-Fe. The elastic properties predicted by the model are in good agreement with those obtained in previous theoretical treatments of paramagnetic phases of iron, as well as with the bulk moduli derived from isothermal compressibility measurements [N. Tsujino et al., Earth Planet. Sci. Lett. 375, 244 (2013)]. Less agreement is found between theoretically calculated and experimentally derived single-crystal elastic constants of gamma- and delta-iron.

Place, publisher, year, edition, pages
American Physical Society, 2017
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-220460 (URN)10.1103/PhysRevB.96.224406 (DOI)000417075100001 ()2-s2.0-85039421203 (Scopus ID)
Funder
VINNOVASwedish National Infrastructure for Computing (SNIC), 2015/16-50
Note

QC 20180103

Available from: 2018-01-03 Created: 2018-01-03 Last updated: 2018-02-27Bibliographically approved
Ehteshami, H. & Ruban, A. V. High-temperature thermophysical properties of γ- and δ-Mn from first principles. Physical Review Materials
Open this publication in new window or tab >>High-temperature thermophysical properties of γ- and δ-Mn from first principles
(English)In: Physical Review Materials, ISSN 2475-9953Article in journal (Refereed) Submitted
National Category
Condensed Matter Physics
Research subject
Materials Science and Engineering; Physics
Identifiers
urn:nbn:se:kth:diva-223664 (URN)
Funder
VINNOVA, 2012-02892
Note

QC 20180228

Available from: 2018-02-27 Created: 2018-02-27 Last updated: 2018-02-28Bibliographically approved
Ehteshami, H., Ruban, A. V. & Korzhavyi, P. .Role of defects in Ti(O,C).
Open this publication in new window or tab >>Role of defects in Ti(O,C)
(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Research subject
Materials Science and Engineering; Physics
Identifiers
urn:nbn:se:kth:diva-223666 (URN)
Funder
VINNOVA, 2012-02892
Note

QC 20180228

Available from: 2018-02-27 Created: 2018-02-27 Last updated: 2018-02-28Bibliographically approved
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