MULT is a semi-empirical package for studying the electronic and geometrical
structure of organic molecules with well-defined "chemical bonds" written by
Andrei M. Tokmachev and Andrei L. Tchougreeff.
The method used in MULT stems from our earlier program sequence known as BF (Boutleroff-Fock) which is based on the trial wave function taken as the antisymmetrized product of strictly localized geminals. The atomic basis is transformed to the hybride one by unitar transformations of one s- and three p-orbitals for every heavy (non-hydrogen) atom. Two hybride orbitals are uniquely assigned to every chemical bond. For every chemical bond the two-electron wave function (geminal) with varying weights of two ionic and one covalent configurations is contsructed. All the parameters of transformation from the atomic basis to the hybride one and the weights of contributions to geminals are determined on the ground of the variational principle. Later this simple scheme has been extended by allowing various types of single-determinant wave functions to be present either for extended π-systems in organic molecules or in, so called, close ligand shells in the metal complexes (like those of Zn(II)) or in hydrogen bonds. Next, the multipole approximation has been applied to make feasible calculation of the subshell-dependent two-center electron-electron interactions in the parameterizations like MNDO and higher of this family. The package MULT calculates the optimal hybrid and molecular orbitals, the coefficients of geminal expansions, and allows to determine the heats of formation of organic molecules. The determination of the minimum on the potential energy surface is also available. Due to geminal usage the method features O(N) dependence of the required computational resourses on the system size.
Source: BF, by Andrei M. Tokmachev and Andrei L. Tchougreeff.
Documentation: A short BF reference is available on-line. More elaborated version is under construction.