J. Chem. Phys. Abstract
Abstract
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
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 profile is
obtained directly from the probability distribution of the
reaction coordinate subspace and, therefore, no unbiasing of the
configuration space or
postprocessing of the output data is required.
The new method is applied to a variety of model problems including a
two-dimensional free energy surface 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.