Classical and ab-initio molecular dynamic simulation of an amorphous silica surface

We present the results of a classical molecular dynamic simulation as well as of an ab-initio molecular dynamic simulation of an amorphous silica surface. In the case of the classical simulation we use the potential proposed by van Beest et al. (BKS) whereas the ab-initio simulation is done with a Car-Parrinello method (CPMD). We find that the surfaces generated by BKS have a higher concentration of defects (e.g., concentration of two-membered rings) than those generated with CPMD. In addition also the distribution functions of the angles and of the distances are different for the short rings. Hence we conclude that whereas the BKS potential is able to correctly reproduce the surface on the length scale beyond approximate to5 Angstrom, it is necessary to use an ab-initio method to reliably predict the structure at small scales. (C) 2002 Elsevier Science B.V. All rights reserved.