We find that the proposed method strikes a reasonable balance between accuracy and cost. Foremost, it significantly expands the application range of additive QM/MM models. The availability of an analytical gradient expression for both the cell parameters and the internal geometries is an important step forward. In dayto-day applications, the AC(1)-QM/MM model can be a useful first approach to crystal packing effects, with negligible added cost relative to single molecule gas phase calculations.