Structural properties of glassy and liquid sodium tetrasilicate: comparison between ab initio and classical molecular dynamics simulations

The structural properties of glassy and liquid sodium tetrasilicate Na2Si4O9 are studied by Car-Parrinello molecular dynamics simulations. The results are compared to those obtained for the same samples by classical molecular dynamics simulations using a Kramer, van Beest and van Santen-type potential. We note that, in the Na2Si4O9 liquid, the ab initio description gives a higher number of defects than the classical one. In particular, comparison between the coordinations, the pair correlation functions and the angle distributions given by the two descriptions are presented. In the Na2Si4O9 glass, the details of the local structure are found to be different in the classical and ab initio descriptions. We show that these differences are related to the modifications of the atomic charges due to the introduction of Na atoms, which are not taken into account in the classical simulations. (C) 2002 Elsevier Science B.V. All rights reserved.