Multipolar third-order non-pairwise additivity of intermolecular forces: Effects on crystal properties and third virial coefficients

Abstract

In this paper we give the results of computing the third virial coefficient and the cohesive energy of the crystal for argon taking into account the higher-order multipole terms in the long-range three- body interaction as recently calculated by Bell. The Barker-Pompe potential has been used as the two-body potential function. We find that the third virial coefficient values for argon computed with this more complete non-additive energy function agree very much better with the experimental values than when only the triple-dipole term is used. This is particularly true at lower temperatures. The results also show that better agreement would be obtained if some form of repulsive non- addivity were included in the computation. For the cohesive energy of the crystal we find that the dipole-dipole-quadrupole energy is one-third as large as the triple-dipole energy and so cannot be neglected in these lattice computations. Furthermore, we find that these higher- order three-body forces do not stabilize the face-centred-cubic lattice for argon, the hexagonal-close-packed lattice having a slightly lower energy.