TIGHT-BINDING COMPUTATIONS OF ELASTIC-ANISOTROPY OF FE, XE, AND SI UNDER COMPRESSION

A tight-binding total-energy model parametrized to first-principles li nearized augmented plane-wave computations is applied to study elastic ity and elastic anisotropy in Fe, Xe, and Si at high pressures. We fin d that the model works well in reproducing the compression, electronic structure, phase relations, and elasticity in these diverse materials . In Xe, for example, the same parametrization works well over a fivef old compression range from a van der Waals solid to a dense metal. We find that the cubic close-packed structures are all more anisotropic t han hexagonal close packed and that at high pressures the elastic anis otropy approaches that of any central force nearest-neighbor model. We find that long-range, nonorthogonal parametrizations are necessary fo r greatest accuracy.