Inherent structure theory of local order in liquid and amorphous alloys. I. The nearly-free-electron case

Abstract

The local order in liquid and amorphous alloys of free-electron-like metals has been systematically studied using a molecular dynamics computer simulation linked to a steepest-descent mapping of the instantaneous configurations of the liquid onto local potential energy minima. Atomic interactions are expressed in terms of volume forces and pair forces derived from linear response theory and optimised first-principles pseudopotentials. A detailed study of the pair correlation functions, bond-angle distributions and structure factors after the mapping confirms the existence of an inherent structure of the liquid independent of temperature and density but sensitive to the details of the interatomic forces. The removal of the thermally induced distortions through the mapping produces a significant image enhancement of the short-range order. Comparison with X-ray and neutron diffraction data and with EXAFS measurements shows that the combination of the molecular dynamics simulation with the steepest-descent projection is a very successful technique for modelling the structure of metallic glasses. The author studies the inherent structure of both glass-forming alloys and those that form stable crystalline compounds and find characteristic similarities and differences. The inherent structure of the compound-forming alloy resembles a highly defective version of the tetrahedrally close-packed crystal. In the glass the local order is again of a tetrahedrally close-packed type but contains a substantially larger number of topological defects.