Automated calculations of exchange magnetostriction

We present a methodology based on deformations of the unit cell that allows to compute the isotropic magnetoelastic constants, isotropic magnetostrictive coefficients and spontaneous volume magnetostriction associated to the exchange magnetostriction. This method is implemented in the python package MAELAS (v3.0), so that it can be used to obtain these quantities by first–principles calculations and classical spin–lattice models in an automated way. We show that the required reference state to obtain the spontaneous volume magnetostriction combines the equilibrium volume of the paramagnetic state and magnetic order of the ground state. In the framework of a classical spin–lattice model, we find that the analysis of volume dependence of this method jointly to the knowledge of the spatial derivative of the exchange interactions can reveal the equilibrium volume of the paramagnetic state and spontaneous volume magnetostriction unambiguously without involving any calculation of the paramagnetic state. We identify an error in the theoretical expression of the isotropic magnetostrictive coefficient λ^α1,0 for uniaxial crystals given in previous publications, which is corrected in this work. The presented computational tool may be helpful to provide a better understanding and characterization of the relationship between the exchange interaction and magnetoelasticity.