Molecular packing for planar molecules

The crystal packing of five planar molecules is considered in this paper. Each unit cell contains two non-equivalent molecules whose planes are inclined to each other. It is shown that the angle of inclination between the planes is completely determined by a simple geometrical criterion. A simple sequential arrangement of the four molecules defining the elementary parallelopiped of which the entire crystal is built leads to various configurations from which the one which has the least interaction energy can be picked out. Using a crude Lennard-Jones potential for the non-bonded interaction and a hard sphere model for the atoms, one can compute the crystal structure from the minimum energy criterion and this is found to be in fair agreement with the observed structure. This simple sequential packing with some modifications can provide an useful model for calculating the radial distribution function in amorphous solids involving planar groups.