Free Energy Calculations for Lennard-Jones Systems
and Water Using the Expanded Ensemble Method. A
Monte Carlo and Molecular Dynamics Simulation Study.
Molecular Physics, v.82, pp.455-471 (1994)
A.P.Lyubartsev
and
Aatto Laaksonen,
Div.of Physical Chemistry, Arrhenius Laboratory, University of
Stockholm,
S-10691, Stockholm, SWEDEN
Pavel N.Vorontsov-Velyaminov,
Physics Faculty, St.Petersburg State University,
198904, St.Petersburg, RUSSIA
Abstract.
The method of expanded ensembles for calculation of free energy in
Monte Carlo simulations (Lyubartsev et.al, J.Chem.Phys.,96,1776,1992) is
incorporated into molecular dynamics simulations. Calculations of the free
energy for the Lennard-Jones system are
carried out using both variants of
the expanded ensemble method (i.e. Monte Carlo and molecular dynamics
simulations) and are shown to give identical results. The free energy for
two variants of the simple point charge (SPC) water model (rigid and flexible)
is calculated using the Lennard-Jones system as a reference. Numerically
very accurate results for the free energy are obtained. The results are in
accordance with results obtained using other methods for calculation of
free energy in computer simulat
ions. The advantages of the presented method
and possible applications for calculation of free energies for more
complicated molecular systems are discussed.
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