  The thermal expansion of pure and Ti-bearing fused silica was estimated using
free energy minimization lattice dynamics calculations in the quasiharmonic
approximation. While the calculations give the expected drop in the coefficient
of thermal expansion in going from quartz to fused silica, the overall shape of
the coefficient of thermal expansion versus temperature curve for the
high-purity and titanium-bearing fused silica is not reproduced by the
quasiharmonic approximation. This result is robust and insensitive to system
size and annealing density of the glass.
