Statistical ensembles and molecular dynamics studies of anisotropic solids. II

We have recently discussed how the Parrinello–Rahman theory can be brought into accord with the theory of the elastic and thermodynamic behavior of anisotropic media. This involves the isoenthalpic–isotension ensemble of statistical mechanics. Nosé has developed a canonical ensemble form of molecular dynamics. We combine Nosé’s ideas with the Parrinello–Rahman theory to obtain a canonical form of molecular dynamics appropriate to the study of anisotropic media subjected to arbitrary external stress. We employ this isothermal–isotension ensemble in a study of a fcc→ close-packed structural phase transformation in a Lennard-Jones solid subjected to uniaxial compression. Our interpretation of the Nosé theory does not involve a scaling of the time variable. This latter fact leads to simplifications when studying the time dependence of quantities.