QuantumClassical Modeling of Chemical Phenomena
CSIC Building (#406),
Seminar Room 4122.
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Speeding up path integral simulations
David Manolopoulos
Oxford University

Abstract:
A quantum simulation of an imaginary time path integral typically requires around n times more computational effort than the corresponding classical simulation, where n is the number of ring polymer beads (or imaginary time slices) used in the calculation. It is however possible to improve on this estimate by decomposing the potential into a sum of slowly and rapidly varying contributions. If the slowly varying contribution changes only slightly over the length scale of the ring polymer, it can be evaluated on a contracted ring polymer with fewer than the full n beads (or equivalently on a lower order Fourier decomposition of the imaginary time path). In this talk, I shall first motivate and outline this ring polymer contraction idea and then show how it can be used to perform fully converged path integral molecular dynamics (PIMD) and ring polymer molecular dynamics (RPMD) simulations of typical empirical water models with little more than classical computational effort in the limit of large system size. We hope that this development will encourage future studies of quantum mechanical fluctuations in liquid water and aqueous solutions and in many other systems with similar interaction potentials. 
