Dispersion effects in SiO2 polymorphs: An ab initio study
Résumé
The effect of electronic dispersion over a wide variety of SiO2 polymorphs (faujasite, ferrierite, α-cristobalite,
α-quartz, coesite, and stishovite) is investigated using state-of-the-art density functional theory. Different
functionals and dispersion correction schemes are compared, ranging from the local density approximation
to fully nonlocal exchange-correlation functionals. It is shown that both empirical dispersion corrections and
fully nonlocal functionals improve the energetics and give correct volumetric data. However, the correct volume
results come from error cancellation between an overestimation of the Si-O distance and an underestimation of
the Si-O-Si angle. Quantum Monte Carlo is used to compute the quartz-cristobalite energy difference within an
accuracy of 0.2 kCal/mol per SiO2 unit. This demonstrates the feasability of achieving subchemical accuracy on
extended systems, and confirms the validity of the Slater-Jastrow ansatz for describing SiO2 polymorphs.