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Perturbative Metropolis Monte Carlo Simulations - a Hybrid QM/MM Approach

Jonas Feldt (Institute of Physical Chemistry, University of Gottingen)
Ricardo A. Mata (Institute of Physical Chemistry, University of Gottingen)

Processes in condensed phase are strongly influenced by environmental effects.
Simulations with Molecular Mechanics (MM) are well established but for many
effects a description of the electronic structure trough Quantum Mechanics (QM)
is necessary. Hybrid QM/MM approaches are routinely used in the recent years.
Molecular Dynamics (MD) coupled with QM/MM requires expensive electronic
structure calculations to compute the energy and gradient at every step.
Although by far most of the degrees of freedom are in the environment many QM
calculations have to be carried out. This limits the simulated time scales as
well as the size of the QM part or the accuracy of the QM method. We propose to
use perturbation theory to decouple the dependency of the QM and MM part based
on work of Truong and Stefanovich[1]. It allows us to independently sample the
configurational space of QM and MM part with Metropolis Monte Carlo (MC)
simulations. Only a limited number of full QM calculations has to be carried
out during a simulation to ensure the accuracy of the perturbation approach.
Furthermore, we brought forward a hybrid implementation utilizing GPUs which
cuts down the computational costs by an order of magnitude[2]. The influence of
the approximations and technical parameters on the results have been thoroughly
investigated. Benchmark studies have been carried out by looking at the solvent
structure, the description of thermodynamics and reactivity in solution and
properties as well as electronic spectra of the solute.

[1] T. N. Troung, E. V. Stefanovich, Chem. Phys. Lett., 256 (1996), 348.
[2] S. Miranda, J. Feldt, R. Mata, N. Roma, P. Tomás, Int. J. High Perform., DOI: 10.1177/1094342016649420, (2016).

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