Spheroidal multipolar expansions for intermolecular energy in crystal theory. Lattice energy and cell dimensions of the orthorhombic structure of benzene crystal

The oblate spheroidal formalism for the interaction energy between two non-overlapping ellipsoidal charge distributions is applied to the determination of the lattice energy and cell dimensions of the orthorhombic structure of benzene crystal. The molecules are assimilated to quadrupolar oblate ellipsoids and the pair potential is assumed to be a sum of two terms: a Kihara core-potential extended to oblate ellipsoids and the spheroidal quadrupolar interaction. The value so obtained for the lattice energy is -51.3 kJ mole^-1 at unit cell dimensions of 7.7, 8.1 and 7.4 A, while the observed heat of sublimation corrected for zero-point vibration is -52.3 kJ mole^-1 and the experimental cell dimensions are 7.39, 9.42 and 6.81 A at 138 K.