BAR-Based Multi-Dimensional Nonequilibrium Pulling for Indirect Construction of QM/MM Free Energy Landscape
2018-11-13T15:29:00Z (GMT)
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<p>Construction of free energy landscapes at Quantum
mechanics (QM) level is computationally demanding. By constructing a thermodynamic
cycle connecting QM states via an alchemical pathway, we can obtain converged
statistics with much less computational resources. The indirect scheme of QM/
molecular mechanics (MM) free energy simulation is often orders of magnitude
faster than direct QM/MM simulations. Previous reports on indirect QM/MM
simulations are mostly equilibrium sampling based and nonequilibrium methods
are only exploited in one-dimensional alchemical QM/MM end-state correction at
two end states. In the current work, we report a multi-dimensional nonequilibrium
pulling scheme for indirect QM/MM free energy simulations, where the whole free
energy simulation is performed only with nonequilibrium methods. The collective
variable (CV) space we explore is the combination of one alchemical CV and one
physically meaningful CV. The current nonequilibrium indirect QM/MM simulation
method can be seen as the generalization of equilibrium perturbation based
indirect QM/MM methods. The test systems include one backbone dihedral case and
one distance case. The two cases are significantly different in size, enabling
us to investigate the dependence of the speedup of the indirect scheme on the
size of the system. It is shown that the speedup becomes larger when the size
of the system becomes larger, which is consistent with the scaling behavior of
QM Hamiltonian. </p>
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