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

A new computational method is proposed for ab initio 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 (MTS) algorithm and an approximate QM/MM Hamiltonian derived from the first-order Rayleigh–Schrödinger perturbation theory (PT) 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 one quantum mechanical (QM) molecule and 255 molecular mechanical (MM) molecules and discuss the advantages in calculating statistical averages such as radial distribution and heat of solution.