Elastic constants of cubic crystals

• We report a new code for the calculation of the elastic constants of cubic systems.
• This code is reliable because it uses single deformation instead of rhombohedral strain.
• The elastic constants of various cubic crystals are calculated to show the effectiveness of the code.

In this paper we present details of our developed open source software, cubic-elastic  , for the calculation of the elastic constants (ECs) of cubic crystals. The comparison of the calculated ECs for various types of cubic systems by this software with those from the other available softwares as well as experimentally measured results confirms that our code can predict reliable results. The success of our code originates from its use of single deformation. The other codes usually use rhombohedral strain (RS). RS leads to 3B0+4C443B0+4C44 expression. Hence, RS systematically adds error to the C44 through the bulk modulus calculations, and thereby may not be mathematically an appropriate approach. The total energy is accurately calculated by the WIEN2k within the highly accurate full-potential (linearized) augmented plane-waves plus local orbitals method. The ECs are calculated by the second-order derivatives of the fitted polynomials to the calculated total energies with respect to the elements of strain tensors at zero strains. We have presented the theoretical background and methodology of the cubic-elastic. We have validated the software by taking a variety of cubic samples into consideration and calculated their ECs. The zero bulk error calculations show that the results obtained from the cubic-elastic   are in good agreement with the available experimental data and the previous theoretical results and predicts the sign of elastic constants correctly. The calculated Cauchy’s pressure (C″C″) and Poisson’s ratio (ν) of LaS predict that it is an ionic compound. This prediction is in agreement (disagreement) with the previous ionic (covalent) bonds prediction deduced from previous ν   (C″C″).

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