Classical and ab initio molecular dynamics of quartz surfaces

COMP 173

Alexander D. MacKerell Jr., and Pedro E. M. Lopes, Department of Pharmaceutical Sciences, University of Maryland, 20 Penn Street, Baltimore, MD 21201
Silica dusts are known to be toxic and cause lung disease-silicosis. Little is known about the actual mechanism and we have applied computational techniques to Quartz surfaces to address the problem. Two distinct surfaces were used, (011) and (100), characterized by single and geminal OH groups when fully protonated. Classical molecular dynamics was used to study the interaction of the model surfaces with slabs of water. Newly developed CHARMM parameters were first validated by comparing theoretical results of water confined between two silica slabs with experimental VDOS spectra. Ab initio molecular dynamics were performed on homolitically cleaved surfaces exposing Si-O groups. Very different behaviours were found between (011) and (100) surfaces. Whereas on (011) reconstruction is very fast, taking place in less than 600fs, on (100) after 2ps some Si-O radicals remain unreacted. It is expected that these groups are very reactive towards water, forming the full hydroxylated surface. On the other hand, the groups formed on (011), might be stable towards reaction with water and play a role in the toxicity of quartz.