to use energetic and geometric data from experimental sources . Geometric data for a wide variety of structures are readily available from the Crystal Structure Database (CSD) which recently surpassed one million entries . The geometries of these crystal structures are typically determined from experimental methods such as neutron diffraction, or more commonly, single crystal or powder X-Ray Diffraction (XRD). With the exception of hydrogen atoms resolved by XRD, the uncertainties in experimentally determined geometries are expected to be small. When used directly within CSP force-field parameterization, some error might propagate from neglecting the thermal expansion of the crystal at finite temperatures. Fortunately, these effects are generally considered to be quite minor.