The large cost of DFT calculations has resulted in pairwise atom-atom force fields with simple functional forms and multipole electrostatics remaining a fundamental part of CSP methods. Indeed, because of the high number of crystal structures that must be evaluated, the initial energy surface that is sampled during the first stage of organic CSP is inevitably a force field energy surface. The effectiveness of CSP in finding good geometric matches to experimental structures thus reflects the generally good structures generated by these force fields. The relative energies calculated using the force fields applied during structure generation are equally important and, if not the final energies themselves, are the basis for selecting structures for further, higher level calculations. Therefore, it is desirable that these computationally cheaper methods are still as accurate as possible.