quantum mechanical/molecular mechanical molecular dynamics using multiple-time-scale approach and perturbation theory

Shiga, Motoyuki   ; Tachikawa, Masanori*

A new computational method is proposed for quantum-mechanical/molecular-mechanical (QM/MM) molecular dynamics (MD) which is limited to time-independent thermodynamic analysis. The idea is to use the mass-scaling method combined with multiple-time-scale algorithm and an approximate QM/MM Hamiltonian derived from the first-order Rayleigh-Schroedinger perturbation theory in which the electronic polarization is neglected as a first approximation. If the polarization effect is not so strong, the correction can also be considered after the simulation run using the weighted sampling method. The advantage and disadvantage of the method is discussed in terms of its computational efficiency and accuracy. As a simple example, we demonstrate an MD simulation of liquid water containing 1 QM molecule and 255 MM molecules, and discuss the advantages in calculating statistical averages such as radial distribution and heat of solution.