Ring Polymer Molcular Dynamics with Gaussian Thermostats

Orateur : Martin NEUMANN (Faculty of Physics, University of Vienna, Austria)

Two crude yet sometimes surprisingly successful approaches to obtain dynamical information on quantum many-body systems are Centroid Molecular Danamics and Ring Polymer Molecular Dynamics. Both are related to the Path Integral Monte Carlo method for calculating static properties, whereby each quantum particle is replaced by a classical ring polymer of P copies of the original particle which are connected by harmonic springs. While PIMC becomes exact as the Trotter number P goes to infnity, the assumption of CMD is that solving the classical equations of motion for the ring polymers’ centers of mass (centroids) under the influence of quantum mechanical forces allows one to calculate approximate time correlation functions for the quantum system. Although also possible with CMD, a technical feature inherent to RPMD is that the averaging over the polymers’ internal coordinates is also performed by classical molecular dynamics. However, due to the stiffness of the springs linking the momomers, care must be taken to achieve an efficient averaging over the polymers’ modes, and this is usually done by using normal coordinates and chains of Nose-Hoover thermostats. Here, we will investigate whether using primitive coordinates and employing a set of parameterless Gaussian thermostats provides a viable alternative.

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