Tight binding molecular dynamics studies of the viscosity of liquid selenium

Abstract

A tight binding technique is employed to study theinfluence of the size of the unit cell on molecular dynamics simulationsof liquid selenium at 870 K. Systems with 69, 138, 276 and 552 atomshave been studied within the Fermi operator expansion method. TheGreen-Kubo formula has been used to calculate the shear viscosity forall systems from the off-diagonal component of the stress tensor. Nodependence on the cell size could be found within the error bars definedby statistical accuracy. For the two smallest systems calculations up to60 ps have been performed where the viscosities become identical. Thesefindings indicate that the recently reported disagreement of DFTcalculations and experiments on the viscosity of liquid selenium at 870K must be attributed to a deficiency in the chosen exchange correlationfunctional rather than size effects.