To address this issue, electronic structure calculations are typically combined with molecular mechanics sampling of the potential energy surfaces of the host-guest system. These combined protocols usually involve two stages: i) perform a molecular dynamics or Monte Carlo sampling with classical force fields on a combined guest-host system (which can easily comprise tens of thousands atoms or more) and ii) conduct QM calculations on snapshots taken from the MD trajectory. In the second stage, the host molecules can be treated as the MM region in QM/MM calculations to include the electrostatic effects of the environment, whilst reducing the computational cost. With recent advances in linear-scaling density functional theory software, it is also possible to treat the entire system quantum mechanically in the evaluation of excited state properties of snapshots of the system. 17 However, in all cases, step i) above requires the use of approximate molecular mechanics force fields to sample the dynamics of the system in the condensed phase.