MAELAS 2.0: A new version of a computer program for the calculation of magneto-elastic properties

MAELAS is a computer program for the calculation of magnetocrystalline anisotropy energy, anisotropic magnetostrictive coefficients and magnetoelastic constants in an automated way. The method originally implemented in version 1.0 of MAELAS was based on the length optimization of the unit cell, proposed by Wu and Freeman, to calculate the anisotropic magnetostrictive coefficients. We present here a revised and updated version (v2.0) of MAELAS, where we added a new methodology to compute anisotropic magnetoelastic constants from a linear fitting of the energy versus applied strain. We analyze and compare the accuracy of both methods showing that the new approach is more reliable and robust than the one implemented in version 1.0, especially for non-cubic crystal symmetries. This analysis also helps us find that the accuracy of the method implemented in version 1.0 could be improved by using deformation gradients derived from the equilibrium magnetoelastic strain tensor, as well as potential future alternative methods like the strain optimization method. Additionally, we clarify the role of the demagnetized state in the fractional change in length, and derive the expression for saturation magnetostriction for polycrystals with trigonal, tetragonal and orthorhombic crystal symmetry. In this new version, we also fix some issues related to trigonal crystal symmetry found in version 1.0. Program summary Program title: MAELAS CPC Library link to program files: https://doi.org/10.17632/gxcdg3z7t6.2 Developer's repository link: https://github.com/pnieyes2019/MAELAS Code Ocean capsule: https://codeocean.com/capsule/2689126 Licensing provisions: BSD 3-clause Programming language: Python3 Journal reference of previous version: P. Nieves, S. Arapan, S.H. Zhang, A.P. K4dzielawa, R.F. Zhang and D. Legut, Comput. Phys. Commun. 264, 107964 (2021) Does the new version supersede the previous version?: Yes Reasons for the new version: To implement a more accurate methodology to compute magnetoelastic constants and magnetostrictive coefficients, and fix some issues related to trigonal crystal symmetry. Summary of revisions: New method to calculate magnetoelastic constants and magnetostrictive coefficients derived from the magnetoelastic energy. Correction of the trigonal crystal symmetry. Implementation of the saturation magnetostriction for polycrystals with trigonal, tetragonal and orthorhombic crystal symmetry. In the visualization tool MAELASviewer, we included the possibility to choose the type of reference demagnetized state in the calculation of the fractional change in length. Nature of problem: To calculate anisotropic magnetostrictive coefficients and magnetoelastic constants in an automated way based on Density Functional Theory methods. Solution method: In the first stage, the unit cell is relaxed through a spin-polarized calculation without spin-orbit coupling (SOC). Next, after a crystal symmetry analysis, a set of deformed lattice and spin configurations are generated using the pymatgen library [1]. The energy of these states is calculated by the Vienna Ab-initio Simulation Package (VASP) [2], including SOC. The anisotropic magnetoelastic constants are derived from the fitting of these energies to a linear polynomial. Finally, if the elastic tensor is provided [3], then the magnetostrictive coefficients are also calculated from the theoretical relations between elastic and magnetoelastic constants. Additional comments including restrictions and unusual features: This version supports the following crystal systems: Cubic (point groups 432, (4) over bar 3m, m (3) over barm), Hexagonal (6mm, 622, (6) over bar 2m, 6/mmm), Trigonal (32, 3m, (3) over barm), Tetragonal (4mm, (4) over bar 22, 42m, 4/mmm) and Orthorhombic (222, 2mm, mmm). (C) 2021 Elsevier B.V. All rights reserved.