The directional contact distance of two ellipsoids: Coarse-grained   potentials for anisotropic interactions
  We obtain the distance of closest approach of the surfaces of two arbitrary ellipsoids valid at any orientation and separation, measured along their inter-center vector. This directional distance is derived from the Elliptic Contact Function. The geometric meaning behind this approach is clarified. An elliptic pair potential for modelling arbitrary mixtures of elliptic particles, whether hard or soft, is proposed based on this distance. Comparisons to Gay-Berne potentials are discussed. Analytic expressions for the forces and torques acting on the elliptic particles are given. 
Leonid Paramonov and S.N. Yaliraki