Intermolecular potential Stockmayer

For polar molecules, the most widely used intermolecular potential energy is the Stockmayer Potential ... 

Another useful intermolecular potential is the Stockmayer potential [178,379], which can be used to describe the interaction between polar molecules. The functional form of the Stockmayer potential is... 

Fig. 12.5 Illustration of the orientation angles used in the Stockmayer intermolecular potential. Molecule j consists of atoms A and B, and molecule i consists of atoms C and D. The vector ry runs from the center of mass of molecule i to the center of mass of molecule j. The vector JTJ gives the orientation and magnitude of the dipole moment of molecule i, with a similar definition for JTj. A ghost copy of molecule j is shifted to left to more easily visualize the orientation angle ifr. See Eqs. 12.11 to 12.13 and accompanying text for definition and description of these angles.

One of the simplest orientational-dependent potentials that has been used for polar molecules is the Stockmayer potential.48 It consists of a spherically symmetric Lennard-Jones potential plus a term representing the interaction between two point dipoles. This latter term contains the orientational dependence. Carbon monoxide and nitrogen both have permanent quadrupole moments. Therefore, an obvious generalization of Stockmayer potential is a Lennard-Jones potential plus terms involving quadrupole-quadrupole, dipole-dipole interactions. That is, the orientational part of the potential is derived from a multipole expansion of the electrostatic interaction between the charge distributions on two different molecules and only permanent (not induced) multipoles are considered. Further, the expansion is truncated at the quadrupole-quadrupole term. In all of the simulations discussed here, we have used potentials of this type. The components of the intermolecular potentials we considered are given by ... 

The intermolecular potential consists of the sum of Eqs.(176) and (177). This simulation was done for 216 and 512 molecules. However, only the autocorrelation functions from the 512 molecules case are discussed here. The small dipole moment of carbon monoxide makes the orientational part of this potential so weak that molecules rotate essentially freely, despite the fact that this calculation was done at a liquid density. The results for the Stockmayer simulation serve the purpose of providing a framework for contrasting results from more realistic, stronger angular-dependent potentials. 

---