|The X-Pol method, initially called the MODEL theory, is a general, and rigorously defined theory,
which can be used either as an electronic structure method for macromolecular
systems or as a quantum force field for biomolecular and materials simulations.
Depending on the problem of interest or one's personal flavor,
ab initio and semiempirical molecular orbital theory
or density functional theory can be used uniformly or in a hybrid.
The X-Pol theory is based on a hierarchy of three approximations.
They were first introduced in 1997,
subsequently used for Monte Carlo and molecular dynamics simulations of
liquid water, liquid
hydrogen fluoride, and a fully solvated BPTI protein,
and a summary of these principles
was recently outlined in
Lingchun Song, Jaebeom Han, Yen-lin Lin, Jiali Gao,
Journal of Physical Chemistry A, 2009, 113, 11656.
Each approximation allows a significant reduction of computational
costs and the introduction of a set of parameters to be
optimized to strive for accuracy.
The X-Pol potential for macromolecular systems is being developed collaboratively
between the groups of Professor Gao and
Professor Don Truhlar.
The feasibility of the X-Pol potential for modeling
has been recently demonstrated.