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) center dot 2H(2)O, and the untraditional H-interacted one, trans-PtCl2(NH3)(N-glycine)center dot H2O. The obtained molecular structures in crystal much better agree with the experimental ones than the optimized ones of the isolated cluster calculation. (c) 2012 Elsevier B.V. All rights reserved.