Molec. Sim. Abstract
Abstract
Adiabatic dynamics methods are employed in a variety of contexts in molecular
dynamics. These include path integral and centroid molecular dynamics
for studying quantum nuclear motion and ab initio molecular
dynamics for studying chemically active systems.
Here, a new molecular dynamics method for calculating free energy profiles for rare events
is presented. The new method is based on the creation of an adiabatic separation between
the reaction coordinate subspace and the remaining degrees of
freedom within a molecular dynamics run. This is achieved by associating with
the reaction coordinate(s) a high temperature and large mass,
thereby allowing the activated process to occur while permitting
the remaining degrees of freedom to respond adiabatically. In this
limit, by applying a formal multiple time scale
Liouville operator factorization, it can be rigorously shown that the
free energy profiles are
obtained directly from the probability distribution of the
reaction coordinate subspace and, therefore, require no
postprocessing of the output data.
The new method is applied on a variety of model problems and
its performance tested against free energy calculations
using the ``bluemoon ensemble'' approach. The comparison shows that
free energy profiles can be calculated with greater ease and efficiency
using the new method.