Dj. Willock et al., THE RELAXATION OF MOLECULAR-CRYSTAL STRUCTURES USING A DISTRIBUTED MULTIPOLE ELECTROSTATIC MODEL, Journal of computational chemistry, 16(5), 1995, pp. 628-647
We describe a method for minimizing the lattice energy of molecular cr
ystal structures, using a realistic anisotropic atom-atom model for th
e intermolecular forces. Molecules are assumed to be rigid, and the st
ructure is described by the center of mass positions and orientational
parameters for each molecule in the unit cell, as well as external st
rain parameters used to optimize the cell geometry. The resulting prog
ram uses a distributed multipole description of the electrostatic forc
es, which consists of sets of atomic multipoles (charge, dipole, quadr
upole, etc.) to represent the lone pair, pi electron density, and othe
r nonspherical features in the atomic charge distribution. Such ab ini
tio based, electrostatic models are essential for describing the orien
tation dependence of the intermolecular forces, including hydrogen bon
ding, between polar molecules. Studies on a range of organic crystals
containing hydrogen bonds are used to illustrate the use of this new c
rystal structure relaxation program, DMAREL, and show that it provides
a promising new approach to studying the crystal packing of polar mol
ecules. (C) 1995 by John Wiley and Sons, Inc.