Ab initio calculations of pressure-dependence of high-order elastic constants using finite deformations approach

Description of elasticity of iron at the ultrahigh pressures is a challenging task for physics, with a potential strong impact on other branches of science. In the present work, we calculate the elastic properties of hcp iron in the pressure range of 50-340 GPa beyond the linear elasticity approximation, conventionally assumed in theoretical studies. We define the higher order elastic constants and present expressions for the long-wave acoustic modes Grüneisen parameters of a compressed hcp crystal. We obtain the second and third order elastic constants of the hcp Fe in the considered pressure interval, as well as its Grüneisen parameters for the highsymmetry directions. The latter are directly compared with the Grüneisen parameters derived from the volume dependences of the vibrational frequencies calculated in the quasiharmonic approximation. The obtained results are used for the stability analysis of the hcp phase of iron at high pressures.

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“…A detailed description of the computational scheme and convergence issues of the used methodology can be found in Ref. [24].…”

Section: Details Of Calculationsmentioning

confidence: 99%

“…In the present work we employ a technique of higher order elastic constants calculations for compressed crystals [23,24]. The full set of SOECs and TOECs of ε-Fe in the pressure interval 50-340 GPa is calculated at temperature T = 0 K. The DFT is used for the calculations of energy at different volumes and deformations.…”

Section: Introductionmentioning

confidence: 99%

Nonlinear elasticity of ɛ -Fe: The pressure effect

Krasilnikov¹,

Lugovskoy

Dikan

et al. 2019

Phys. Rev. B

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“…The author of the Comment [1] would be right if one discuss a general case of deformations including rotations. However, the author overlooked the fact that in our paper [2] we discuss the crystal energy that changes only due to deformations and is invariant with respect to rotations of the crystal as a whole. This is a standard case in solid state physics, in which only symmetric deformations are considered.…”

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confidence: 99%

“…(13) in our Ref. [2]. Taking into account the fourth order term, we can derive an expression for ij α corresponding to Eq.…”

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confidence: 99%