Proposal of new QM/MM approach for geometry optimization of periodic molecular crystal: Self-consistent point charge representation for crystalline effect on target QM molecule

We wish to propose a QM/MM method to analytically optimize structure of periodic molecular crystal. Considering that the whole crystal consists of equivalent subunits, we construct the Fock matrix and evaluate the energy derivatives under the condition that the MM charge distribution is self-consistently determined by the corresponding QM subunit. This QM/MM approach is applied to the periodic molecular crystals of the traditional O-coordinated system, Pt ( CN ) 4 · 2 H 2 O , and the untraditional H-interacted one, trans- PtCl 2 ( NH 3 ) (N-glycine) · H 2 O . The obtained molecular structures in crystal much better agree with the experimental ones than the optimized ones of the isolated cluster calculation.