Pair potential dipolar fluids

Here cr is the collision diameter and e is the depth of the potential well at the minimum of zz(r). For molecules we often use combinations of atomic pair potentials, adding several body potentials that describe bending or torsion when needed. For dipolar fluids we have to add dipole-dipole interactions (or, in a more sophisticated description. Coulomb interactions between partial charges on the atoms) and for ionic solutions also Coulomb interactions between the ionic charges. 

One clever approach to obtaining better convergence is to include asymptotic properties of the pair correlation functions (Lebowitz and Percus 1963). In particular, exact asymptotic expressions have been obtained by Attard and coworkers (Attard 1990 Attard et al. 1991), such as for dipolar fluids. Other work has extended simulation results for a system with a truncated potential to give those for the full potential (Lado 1964). The effects on pair distribution functions of potential truncations are important. 

The very fact that (Pyx) is non zero indicates structural distortion of the fluid which manifests by an anisotropic pair distribution function g(r,y) compressed in the xy plane along axes at angles (p = 124° (0 angle between the projection of r/r onto the xy plane and the ex axis) and most elongated along 0 34°. At the value of the dipole moment yx = 1.955 considered no strong orientational order is observed and the distortion of the fluid structure results mainly from the LJ part of the potential and is only weakly influenced by the dipolar contribution. 

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