New Extensions to Symmetry-adapted Perturbation Theory: Spin Splittings, Explicitly Correlated Dispersion, and Intramolecular Interactions

Auburn University, Auburn AL

Investigators

Abstract

Professor Konrad Patkowski of Auburn University is supported by an award from the Chemical Theory, Models, and Computational Methods program in the Division of Chemistry to develop new computational methods that extend the capabilities of calculating weak interaction energies between molecules. These methods combine high accuracy with interpretive power, providing insight into the physical origins of interactions between molecules. This kind of insight is aids in the understanding, simulation, and rational design of interactions that play key roles in chemistry, physics, biochemistry, and materials science. The new methods developed by Patkowski and his group, which are being implemented in an open-source computer program, are useful for describing interactions relevant to atmospheric chemistry, molecular magnetism, and transition metal catalysis. They also provide a new route to quantifying and interpreting interactions between different fragments of the same molecule, such as those that control the three-dimensional structure of proteins and nucleic acids. In addition, Patkowski continues to develop hands-on computational chemistry modules within the framework of the Auburn University Summer Science Institute, providing realistic research experiences to high-school students and enhancing their awareness of careers in science. He is also facilitating course redesign workshops for Auburn University faculty to facilitate active learning techniques into their classes. The approaches developed by Professor Patkowski and his group extend the symmetry-adapted perturbation theory (SAPT) method for calculating interaction energies between molecules in terms of electrostatic, induction, dispersion, and exchange interactions. In its most common closed-shell formulation, SAPT is widely used to construct intermolecular potential energy surfaces, interpret, and compare the origins of bonding for different complexes and structures, and aid in the construction of force fields. Patkowski is developing three new approaches that enhance the basis set convergence of existing SAPT treatments through an explicitly correlated framework. This will extend the method to complexes in low-spin states by building explicit spin-flip excitations into the exchange energy expressions, and open up a new avenue of application to intramolecular noncovalent interactions, based on range separation of the Coulomb potential rather than fragmentation of the system. Applications of the newly constructed SAPT variants include the elucidation of spin splittings in organic ferromagnets, radical cation-radical anion interactions, and pancake-bonded dimers, the refinement of benchmark energy component databases for force field fitting and classification of complexes according to interaction types. This enables the quantitative description of intramolecular interactions responsible for the stability of sterically crowded molecules and the conformational profiles of molecular balances. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.