Quantum mechanical force field for water with explicit electronic polarization

Abstract

A quantum mechanical force field (QMFF) for water is described. Unlike traditional approaches that use quantum mechanical results and experimental data to parameterize empirical potential energy functions, the present QMFF uses a quantum mechanical framework to represent intramolecular and intermolecular interactions in an entire condensed-phase system. In particular, the internal energy terms used in molecular mechanics are replaced by a quantum mechanical formalism that naturally includes electronic polarization due to intermolecular interactions and its effects on the force constants of the intramolecular force field. As a quantum mechanical force field, both intermolecular interactions and the Hamiltonian describing the individual molecular fragments can be parameterized to strive for accuracy and computational efficiency. In this work, we introduce a polarizable molecular orbital model Hamiltonian for water and for oxygen-and hydrogen-containing compounds, whereas the electrostatic potential responsible for intermolecular interactions in the liquid and in solution is modeled by a three-point charge representation that realistically reproduces the total molecular dipole moment and the local hybridization contributions. The present QMFF for water, which is called the XP3P (explicit polarization with three-point-charge potential) model, is suitable for modeling both gas-phase clusters and liquid water. The paper demonstrates the performance of the XP3P model for water and proton clusters and the properties of the pure liquid from about 900 × 10 6 self-consistent-field calculations on a periodic system consisting of 267 water molecules. The unusual dipole derivative behavior of water, which is incorrectly modeled in molecular mechanics, is naturally reproduced as a result of an electronic structural treatment of chemical bonding by XP3P. We anticipate that the XP3P model will be useful for studying proton transport in solution and solid phases as well as across biological ion channels through membranes. © 2013 AIP Publishing LLC.

Quantum mechanical force field for hydrogen fluoride with explicit electronic polarization

“…58,59 Three key modifications were introduced in PMO. Since the method has been reported in detail previously, 35,[51][52][53] we only provide a brief summary of its key departures from MNDO.…”

“…At present, three different variations of the PMO method have been reported, PMOv1, 52 PMO2, 53 and PMOw, 35 none of which contain parameters for fluorine. The variant of PMO for which we have decided to introduce the F parameters is the PMOw model, having kept all other parameters fixed to those reported in Ref.…”

“…The variant of PMO for which we have decided to introduce the F parameters is the PMOw model, having kept all other parameters fixed to those reported in Ref. 35.…”

“…12 This was a departure from previous models, which employed a H-F bond length of 0.917 Å for the monomer in the gas phase. 11 In 2000, a more extensive set of experimental data for two liquid and four supercritical states of DF was reported by Pfleiderer and co-workers, a molecular orbital derived empirical potential for liquids (MODEL), 30,31 has been subsequently called the explicit polarization (X-Pol) theory, [32][33][34] and has been used in studies of liquid water 35 and a molecular dynamics simulation of a solvated protein. 36 In the study of Wierzchowski et al 29 (henceforth referred to as the previous study), the semiempirical AM1 model 37 was used to represent the individual monomers in the liquid, and the polarization of the molecular wave function of each HF molecule by the surrounding monomers was directly incorporated into the one-electron Hamiltonian.…”

“…The PMO Hamiltonian has been successfully used to develop a quantum mechanical force field within the X-Pol framework for liquid water called XP3P. 35 In addition, we have employed an alternative population analysis for calculating partial charges, called the dipolepreserving polarization consistent (DPPC) charge method, 54 which reproduces the total molecular dipole moment of each monomer from quantum mechanical calculations, eliminating the need for the charge scaling parameter in previous X-Pol simulations. Finally, the model has been parameterized using experimental data not available at the time of the previous study, 8,9 and has employed the optimized H-F bond length of 0.930 Å.…”