A HYBRID SEMIEMPIRICAL QUANTUM-MECHANICAL AND LATTICE-SUM METHOD FOR ELECTROSTATIC INTERACTIONS IN FLUID SIMULATIONS

A method is described to incorporate the Ewald lattice-sum method into quantum mechanical calculations in hybrid quantum and molecular mecha nical (QM/MM) fluid simulations. The procedure is illustrated through standard free energy perturbation calculations in the context of Monte Carlo simulations. The free energy of hydration of chloride ion was c omputed using the hybrid QM/MM-Ewald method, and comparison was made t o results obtained with standard spherical cutoff, The results indicat e that the hybrid QM/MM-Ewald method can be effectively used to includ e long-range electrostatic interactions in quantum mechanical calculat ions of condensed media. (C) 1997 American Institute of Physics.