Anisotropic atom-atom potnetials from X-ray charge densities: application to intermolecular interactions and lattice energies in some biological and nonlinear optical materials

摘要

Anisotropic atom-atoro potentials based onX-ray molecular charge densities are applied in the evaluation of intermolecular interactions and lattice energies of crystals of glycylglycine, DL-histidine and DL-proline, p-nitroaniline and p-amino-p'- nitrobiphenyl. In parallel, calculations are performed on the molecular dimmers (B3L YP) and on the periodic crystals with both Hartree-Fock (HF) and density functional theory (OFT) methods. The dirner interaction energies agree well with the X- ray based values, except for the strongest interactions, which occur in the glycylglycine crystal and for p-amino-p'-nitrobi~ phenyl. The lack of agreement in these cases is attributed to the strong induced polarization of the molecular charge densities. which is not reproduced adequately by the dimmer calculations.The lattice energies are evaluated as1he difference between the molecular interaction energy in the crystal and the molecular relaxation energy upon sublimation. For a given crystal, each of the terms is quite different when calculated with the Periodic HF (PHF) or Periodic OFT (POFT) methods, but the differences are such that the total lattice energies are similar. The agreement between lattice energies derived from the experimental charge densities and those obtained from the PHF and PDFf calculations is within better than, respectively, 10 and 25 kJlrool for glycylglycine, DL-histidine and DL-proline. However. while the experimental charge density approach give reasonable estimates of the lattice energies of p-nitroaniline and p-amino-p'-nitrobiphenyl, the PHF and PDFT calculations fail to predict the stability of these crystals.