Diffusion, Relaxation, And Aging Of Liquid And Amorphous Selenium

Relaxation and aging rates of amorphous selenium and its undercooled melt are calculated by molecular dynamics based on an interaction model derived from density functional calculations. After a fast initial relaxation immediately following the quench, the decrease of diffusivity and the simultaneous increase of dynamic heterogeneity follow an exponential law given by defect annihilation. As observed previously in a Lennard-Jones glass, the non-Arrhenius aging of atomic volume and energy is determined by the time dependence of the diffusivity. The aging time is determined for long times by the diffusivity and diverges exponentially with decreasing temperature. Amorphous selenium differs from metallic glasses in that the breaking of covalent bonds is important for the long time decay of the intermediate self-scattering function (ISSF). Surprisingly for the temperatures investigated, aging of the relaxation times of the ISSF and the bond decay follow the aging of the diffusivity.