The first tests to our model were carried out on the X23 benchmark set (Figure ) introduced by Oterode-la-Roza and Johnson 61 and expanded by Reilly and Tkatchenko. It provides 23 small to medium sized molecular crystals with well known structure and thermochemistry data and covers a range of crystals from van der Waals (vdW) dominated systems to strongly hydrogen bonded ones. For all crystals, the experimental structure was relaxed, optimising the internal geometry as well as the cell parameters. These were optimised without symmetry constraints, as previously noted.