Modeling and experimental studies of neat and metal-doped stishovite, coesite, and quartz under high pressure.*

The results of a comparative study of neat and doped silicon dioxide polymorphs (Fe, Ni or Cu) obtained by density functional theory (DFT) at 0 K and at ambient pressure, 10 GPa, and 20 GPa are presented. The metal atoms are introduced at substitutional and octahedral interstitial sites of the crystal, and the relaxed structures are analyzed and ranked according to total energy. Changes in the enthalpy of the neat and doped crystals are estimated at selected temperatures using quantum mechanics molecular dynamics (DFT-MD). We report the modeled enthalpy of the neat and doped crystals, as well as the dependency of the unit-cell parameters, band gaps, and Raman-active modes on pressure, and compare some of these results to those obtained experimentally using a diamond anvil cell. In addition, we present our search results of the high-pressure phases of silicon dioxide using DFT-based evolutionary simulations and report on the stability of the silica phases, as evaluated by convex-hull construction.