Model Structures and Electron Density Distributions for the Silica Polymorph Coesite at Pressure: An Assessment of OO Bonded Interactions

Abstract

The crystal structure and the bond critical point, bcp, properties of the electron density distribution for the high-pressure silica polymorph coesite were generated for pressures up to ∼17 GPa, using first-principles calculations. The nonequivalent SiO bond lengths and the SiOSi and OSiO angles of the generated structures agree with those observed to within ∼1%. With compression, the SiO bond lengths and the variable SiOSi angles of the structures both decrease while the value of the electron density, ρ(rc), the curvatures, and the Laplacian of the electron density distribution at the bond critical points each increases slightly. As found in a recent modeling of the structure of low quartz, the calculated electron density distributions are nearly static and change relatively little with compression. The bcp properties of the model structure agree with those observed at ambient conditions to within ∼10%, on average, with several of the properties observed to correlate with the observed SiO bond lengths, R...