Having resolved the four limiting ternary faces of the system (second-rank simplexes), we may now form the tetrahedron (third-rank simplex). All forms of energy are self-propagating without distortion into the higher rank system, but the excess term defining the effect of the polarization work that depends upon localized partial charges. We anticipated that the simplest procedure is to assume that ionic polarizabilities and interionic distances do vary linearly with composition (see Eqs. 4.46–4.48). The computational approach is thus trivial. Another problem to resolve is the exponential growth of requested energy points with the ranking of the system. We found that a good compromise between accuracy and computational cost is a reduction of the T step from 5 to 10 K and an increase of the compositional step from 0.0005 to 0.001. The number of smoothing cycles is, in terms of computational effort, quite limited, and we kept 20 cycles as a good exercise.