The X-Pol Method

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 biomolecular systems has been recently demonstrated.

The Hamiltonian

The X-Pol Quantal Force Field vs. MM

The Double Self-Consistent Field (DSCF) Algorithm

The Generalized X-Pol Theory


Comparison of X-Pol with other models

Fragment molecular orbital

Weitao Yang's Divide and Conquer