The organic crystal potential: History, development, and today's cost/performance ratios

The basic concepts of chemical thermodynamics, internal energy, enthalpy, entropy and free energy, are briefly reviewed. A survey of methods for the modeling and the calculation of intermolecular potential and forces are described, with their adherence to physical principles and relative costs and performances. The atom–atom method is critically reviewed, with special attention to Coulombic and polarization energies and the lack of penetration contributions. Ab initio and semiempirical methods based on finite integration of electron densities are compared. The use of sublimation energies for the calibration of intermolecular potentials is described at length, with the preparation of a benchmark set of 150 selected experimental values. Fusion and vaporization enthalpies, and crystal vibrational entropies, are examined with possible ways for their estimation. The set of computer programs encoded in the Milano Chemistry Molecular Simulation (MiCMoS) platform are reviewed. The use of computational crystal chemistry for the analysis of crystal properties is illustrated by a detailed comparison of the structures of acetylsalicylic acid and aspirin.