ABSTRACT
Molecular mechanical force fields have been successfully used
to model condensed-phase and biomolecular systems for a half
century. Molecular mechanical force fields are analytic potential
energy functions based on classical mechanical force constants, van
der Waals potentials, electrostatics, and torsional potentials, with
parameters fit to experiment, to quantum mechanical calculations,
or to both. Accurate results can be obtained from simulations
employing molecular mechanics for processes not involving bond
breaking or bond forming. In this chapter, we describe a new
approach to developing force fields; this approach involves the direct
use of quantum mechanical calculations rather than using them as
a training set for classical mechanical force fields. Computational
efficiency is achieved by partitioning of the entire system into
molecular fragments. Since the mutual electronic polarization is
explicitly treated by electronic structural theory, we call this
approach the explicit polarization (X-Pol) method. Strategies and
examples are presented to illustrate the application of X-Pol to
describe intermolecular interactions as a quantum chemical model
and as a force field to carry out statistical mechanical Monte Carlo
and molecular dynamics simulations.
