ES22-Luo

Author: Luo, Chenxing - Applied Physics and Applied Mathematics Department, Columbia University

Title: Ab initio calculation of third-order elastic constants

Abstract: To describe elastic wave propagation in a medium under stress or strain, the second-order elastic constants (SOEC) need to be modified. Early studies have shown this can be accomplished by introducing additional third-order elastic constants (TOEC) [1]. In this study, we reevaluate these accommodations theoretically and provide ab initio verifications. We first examine the effect of hydrostatic stress, i.e., we describe the pressure derivative of SOEC; then, as a more general case, we investigate the modifications needed for the SOEC under hydrostatic and deviatoric stress. We show that in both cases the modifications of the SOEC are linear combinations of SOEC and TOEC. The relationships are tested on NaCl and MgO with ab initio calculated SOEC and TOEC vs. pressure. The methods to compute finite-pressure TOEC are also self-consistently tested.

[1] R. N. Thurston, K. Brugger, Phys. Rev. 133, A1604–A1610 (1964).