In contrast to internal geometries, cell parameters and cohesive energies are strongly dependent on the description of intermolecular interactions. Consequently significant differences between AC(1) and AC(2) level calculations can be found in many cases. The results (Table and Figure ) show some significant trends. For crystals without hydrogen bonds already at the one-body level reasonable cell parameters are obtained. Optimised cell volumes are smaller by up to 9.5% for CO 2 (4.3% on average) while cell lengths are up to 5.3% smaller than experimental values. Cell angles (including those that would be restricted if symmetry was used) generally change by less than 2°with one outlier of 3.5°for pyrazine. In contrast, for hydrogen bonded systems one-body results are much less convincing. Both cell length (up to 11.2% for pyrazole) and volume (up to 14.4% for ammonia) changes are significantly larger than for non-hydrogen bonded systems. Angles change much more (up to 9.6°for pyrazole) as well. Optimised cell volumes in general are smaller than experimental values with the exception of pyrazole, as is to be expected for the lack of thermal expansion in our scheme. A similar trend is found for the cohesive energies at the AC(1)-QM/MM level, see Figure and Table . For systems without intermolecular hydrogen bonds somewhat reasonable energies are obtained. Cohesive energies are systematically overestimated by up to 20.1 kJ•mol -1 for trioxane (8.9 kJ•mol -1 on average) with respect to experimental results. A much stronger overbinding is found for the hydrogen bonded systems, which results in cohesive energies up to 90 kJ•mol -1 lower than experimental values (41.5 kJ•mol -1 on average).