With this improved approach, calculation of the single-phonon rates in the Orbach regime with fixed phonon linewidths show excellent agreement with the experimental rates (Figure ), and, as for the gas-phase calculation, that the rates are positively correlated with the choice of linewidth. However, the dependence on linewidth is far less significant than in the gas phase and decreases when using larger q-point grids: the rates obtained with Γ = 0.1 cm -1 and Γ = 10 cm -1 differ by a factor of ~19 at 60 K in the gas-phase calculations, reducing to factors of Electrostatic embedding potential (a.u.)