Konrad Patkowski, PhD, College of Sciences and Mathematics Faculty and Staff

Professional Experience

Professor

Department of Chemistry and Biochemistry, Auburn University 2021-present

Associate Professor

Department of Chemistry and Biochemistry, Auburn University 2016–2021

Assistant Professor

Department of Chemistry and Biochemistry, Auburn University 2011–2016

Innovation

Theoretical and Computational Study of Weak Intermolecular Interactions

Intermolecular interactions are everywhere. A network of intermolecular hydrogen bonds determines the properties of liquid water and aqueous solutions. Hydrogen bonds, along with other effects such as stacking interactions among aromatic side chains, govern the structure of proteins and the catalytic abilities of enzymes. Even relatively unreactive species, such as noble-gas atoms, exhibit weak mutual attraction through a phenomenon known as dispersion. This attraction is the reason noble gases can form liquids and solids at low temperatures.

In computational studies of interactions between two atoms or molecules, the key quantity is the potential energy surface (PES). This surface represents the electronic interaction energy of the dimer as a function of the distance between the monomers and their relative orientations. Once the PES is known, researchers can calculate spectra, virial coefficients, liquid properties and crystal parameters that can be compared with experimental results.

The interaction energy at a given geometry is often calculated using the supermolecular approach. In this method, a quantum-chemistry electronic-structure theory is used to calculate the energy of the dimer, AB, and the energies of the individual monomers, A and B. The monomer energies are then subtracted from the dimer energy.

This subtraction can be challenging because the interaction energy is often several orders of magnitude smaller than the energies being subtracted. It is comparable to determining a person’s weight by placing that person on a large, fully loaded ship and then measuring the difference between the ship’s weight with and without the person. In addition, the resulting interaction energy is a single value that provides limited insight into the physical origins of the interaction.

A useful alternative is symmetry-adapted perturbation theory (SAPT). SAPT calculates the interaction energy directly, without subtraction, as a sum of low-order terms in a perturbation series. Each term has a clear physical interpretation and corresponds to an electrostatic, induction, dispersion or exchange effect.

Supermolecular and SAPT methods complement one another, and it is often useful to apply both approaches, together with several electronic-structure methods, to construct and interpret accurate potential energy surfaces. As the size of a dimer increases, however, more approximate methods may be necessary. Highly accurate approaches often scale steeply with system size and require substantial processing time and memory, even on powerful supercomputers.

Current Research Topics

• Further development of SAPT methodology and software, particularly for interactions involving open-shell systems such as radicals, transition-metal atoms and transition-metal complexes.

• Computational studies of simple molecules physisorbed on metallic, graphite and graphene surfaces, where binding is governed primarily by dispersion and other intermolecular forces.

• Development and application of highly accurate potential energy surfaces for weakly interacting atoms and small molecules.