Local order in quenched states of simple atomic substances

Abstract

In any fluid or solid condensed phase, instantaneous atomic positions can be resolved into a combination of inherent packing and of vibrational deformation components. In principle the latter can be removed by quenching the system by (mass-weighted) steepest descent on the potential-energy hypersurface. Inherent structures generated this way for a noble-gas model potential have been structurally analyzed, starting both from homogeneous liquid and from heterogeneous crystal-plus-liquid states. Quenched configurations from the homogeneous liquid show that the icosahedral mode of atom coordination is rare; instead, the more appropriate description of inherent structural disorder for the model appears to be variation of coordination number from its most probable value 12. In the case of heterogeneous systems, steepest-descent quenching induces a substantial tendency toward epitaxial crystal growth, incorporating point defects and stacking faults. Nevertheless, mechanically stable packings with side-by-side coexistence of crystalline and amorphous regions still can arise, with energy suggesting that the bonding between the two types of domains is weak.