Computer simulation of the quartz surface: a combined ab initio and empirical potential approach

We investigate several possible reconstructions of the (0 0 1) alpha -quart z surface by using a combinatory approach of classical and ab initio molecu lar dynamics (MD). Configurational space is efficiently explored by fast cl assical MD simulations with a semi-empirical three-body potential, which ha s been shown to be accurate in simulations of the bulk. These runs generate initial structures for further refinement by the accurate quantum MD metho d of Car-Parrinello [P. Car, M. Parrinello, Phys. Rev. Lett. 55 (1985) 2471 ]. Stable reconstructions of the quartz surface have been produced. They sh ow the same pattern: formation of six- and three-membered rings. The same t ype of reconstruction was found in earlier full ab initio calculations [J.M . Rignanese, Ph.D. thesis, 1998]. The obtained structures were found to be local minima in the classical potential, thereby demonstrating the usefulne ss of the empirical potential for surface calculations. This allows for a f ast characterisation of the surface reconstructions and their dynamical pro perties. (C) 2001 Elsevier Science B.V. All rights reserved.