Theoretical Studies of Intermolecular Forces

University Of Delaware, Newark DE

Investigators

Abstract

In this project funded by the Chemical Theory, Models and Computational Methods program in the Division of Chemistry, Professor Krzysztof Szalewicz of the University of Delaware is developing theoretical and computational methods to model and understand intermolecular forces. When two molecules are placed next to each other, each molecule acts on its partner with a weak force that is an order of magnitude weaker than the chemical forces that bind atoms together into molecules. A broad range of physical, chemical, and biological phenomena originate from such intermolecular forces. Knowledge of intermolecular forces is necessary to interpret a variety of phenomena including the structure and function of crystals and proteins. Professor Szalewicz and his coworkers are developing new ideas to improve the modeling of intermolecular forces and to extend their range of applicability. This research is expected to have an impact on metrology standards, energy resource exploration, atmospheric modeling, understanding processes in interstellar clouds, simulating biological phenomena, and predicting the crystalline forms of drugs. These computational approaches are being implemented in software that is freely available to the research community. To predict properties of clusters, biomolecular aggregates, and condensed phases, one needs to know the potential energy surfaces, also called force fields, of the system that describe the possible mutual orientations and separations between molecules. Such surfaces can be computed via ab initio approaches using symmetry-adapted perturbation theory (SAPT). SAPT provides a unique ability to interpret properties dependent on intermolecular forces in terms of the four fundamental physical mechanisms that lead to the electrostatic, exchange, induction, and dispersion contributions to the interaction energies. SAPT is based on monomers described by density-functional theory (DFT), a method denoted as SAPT (DFT), and is as accurate as the regular SAPT but significantly faster. Professor Szalewicz is working to develop SAPT further and increase its range of applicability. and strives to expand SAPT's range of applicability to molecules with hundreds of atoms, a step in the direction of physics-based biomolecular force fields which may bring biomolecular simulations to a new level of reliability.