Simulation of the structure of amorphous silicon dioxide

Abstract

Computer models of amorphous silicon dioxide have been generated by systematic procedures. The models are all stoichiometric, perfectly coordinated and periodic, and composed of ${\mathrm{SiO}}_4$ tetrahedra sharing corners to form a random network. Starting from various random arrangements, each example is subjected to a series of modifications of its connectivity which reduce its potential energy under a valence-force type of potential function. Several examples have been constructed for each of four choices of starting point and method of connectivity modification. The number of silicon atoms in the repeating unit has been varied from 30 to 108, with twice as many oxygen atoms. The force constants have been chosen by comparison with experiment of the computed density and elastic moduli. The calculated neutron scattering of many of the examples is in excellent agreement with recent experiments of high precision. However, examples containing rings of three or four tetrahedra show scattering at small momentum transfer which deviates increasingly from experiment as the numbers of these rings increase.