First-principles simulation on pressure-dependent local structure change of AsS melt

The local structure of AsS melt has been investigated by the first-principles method. At ambient pressure, As4S4 molecules remain in liquid AsS similar to that of crystal As4S4(II). Structural analyses based on the first and second coordination shell indicate that the local structure of AsS melt undergo two sudden change processes with increasing pressure from 0.0 to 6.9 GPa: the first is from 1.5 to 2.9 GPa that the AsS melt transforms from molecular into polymeric liquid, the second is from 4.3 to 5.6 GPa where the coordination number of the first shell for As and S change apparently. Our calculated results and conclusion for the structural change of AsS melt under compression are very different from those of previous report (Phys. Rev. B 84, 224202). Corresponding to the local structure change, the dynamical properties, such as diffusion coefficients and velocity-velocity autocorrelation function, also show apparent transformation in theses pressure intervals. On the basis of the calculated results, we concluded that the local structure changes of AsS melt should be consistent with its liquid-liquid phase transition under compression.