Derivation of MM2 force-field parameters for polychlorophosphazenes (NPCl2)n from ab initio data

Derivation of force-field parameters for chlorophosphazenes was performed through the technique of energy derivatives starting from ab initio calculated data. The SCF method at the 4-31G* level provided the energy surface for the model compound OP2NCl5. The ab initio search of minima (STO-3G*, 4-31G*, 6-31G* basis sets) was also made for the oligomer OP3N2Cl7. The results were compared with those obtained by molecular mechanics including the calculated parameter sets for the MM2 atom types: 25 (P), 9 (N), 7 (O), 12 (Cl). The force-field method improved by the obtained force constants compared quite well with the results produced by the quantum mechanical SCF calculations.