Molecular Dynamics Simulation of Vitreous Silica Structures

Molecular dynamics (MD) simulations can be used to gain insights into the atomic level structure of glasses not easily accessible to experiment. However, to reliably obtain accurate results it is essential to chose the proper force fields (FF), the proper length of the simulation cell, and the proper cooling cycle to generate the 300K structure from the melt. Herein we establish guidelines for these choices. We find that the MS-Q FF and the MSI glass FF both lead to good agreement with the radial distribution function (RDF) from SANS experiments. We find that the simulation cell should contain about 3000 atoms to obtain a density within 1% and accurate RDF, but a cell of 648 atoms leads to a good RDF and a density within 4%. We find that a good compromise between accuracy and reproducibility of results and simulation time is to start with NVT dynamics at 8000K followed by cooling to room temperature at the rate of 100K/2ps. PACS : 61.43.Fs, 64.70.Pf, 61.20.Ja keywords : silica glass, molecular dynamics, force fields, structure, neutron scattering