Quantum mechanical predictions of nonscalar equations of state and nonmonotonic elastic stress-strain relations

Abstract

In continuum mechanics, the isotropic part of the stress deviator (mean pressure) is routinely assumed to depend on the isotropic part of the strain deviator (compression). This assumption was tested using ab initio quantum mechanical calculations of elastic stress as a function of elastic strain and compression. Except for face-centered-cubic elements, the mean pressure varied significantly with shear strain as well as compression. In general, the shear stress did not increase monotonically with elastic shear strain. These phenomena may be important when comparing experimental data obtained on different time scales, particularly when interpreting dynamic response data from short-pulse laser experiments.