ElasT: A toolkit for thermoelastic calculations

We report the improvement and automation of the stress-strain method, which relies on the averaged stresses from ab initio or classical calculations. Stresses obtained from strained crystal lattices at zero and finite temperatures can be directly extracted to fit the strain-stress relationship and get the elastic constants.

Furthermore, the finite-temperature elastic constants can also be obtained by solving a system of overdetermined linear equations directly under constant pressure dynamics (NPT, NPH, etc.) within the stress-strain method, which does not require the equilibrated lattice as a prior condition. It is shown that the elastic constants converge quickly in constant pressure dynamics. This approach proves to be robust and can significantly reduce computational cost.