Our group is conducting research in the area of theoretical and computational chemistry. This is an interdisciplinary field, where chemistry, physics, mathematics, and computer science meet - if you are interested in any (or all) of these fields, come and talk to us!
So what is computational chemistry good for? We can determine exact shape of the molecules, their properties (like dipole moment or polarizability), simulate spectra ranging from UV-VIS through IR and Raman to NMR, find out energy differences and barriers for reactions (from which we can obtain rate and equilibrium constants), calculate forces between molecules and many other useful data. In fact, the only real limitation on what we can obtain is the time it would take to perform the required calculations. And with the speed of computers still doubling about every 18 months, there are always new things to try!
The main focus of our group are studies of the intermolecular interactions in the clusters of small molecules. While intermolecular interactions do not immediately lead to establishment of covalent bonds, they play an important role in orienting and organizing molecules. This in turn may lead (among other effects) to formation of extended structures (such as cell wall or micelle), profound increase of reaction rate (such as in enzymatic reactions or the emerging class of on-water reactions) or in selectivity for one product over another.
Mixed water-methane clusters are an important model for hydrophobic interactions that play central role in description of wide variety of processes, from protein folding to chromatography to formation of methane hydrates. In such large systems (and, in fact, in any cluster formed of three or more molecules) the overall interaction energy cannot be expressed as a sum of interaction energies of all unique pairs of molecules (pairwise-additive terms). Three-body terms, describing interactions among groups of three molecules, represent the leading correction to pairwise-additive approximation. We hope to advance our ability to model complex hydrophobic systems by studying in detail three-body terms in water-methane clusters. First, three-body terms are calculated by state-of-the-art ab initio methods. Second, they are partitioned into the components that have clear physical meaning, such as induction, dispersion, and exchange. Finally, an approximate analytical description for these terms (that can be used in modelling extended systems) is developed based on the physical insight gained earlier.
Pre-reactive complexes of hydroxyl radical (OH) have attracted ample experimental attention in the last decade as precursors of important elementary chemical reactions with wide-reaching implications in atmospheric chemistry. OH radical is the most reactive species in the troposphere. Initial reaction with OH radical is often the rate-limiting step for oxidation of volatile organic compounds (VOCs) by the atmosphere. Consequently, such reactions play crucial role in formation and dissipation of smog, removal of methane (a greenhouse gas) from atmosphere, polymer aging and degradation, etc. Yet very little is known about structure, energetics, and dynamics of complexes formed between OH radical and organic compounds prior to the reaction. We plan to investigate low-lying electronic states of several of these pre-reactive complexes to offer an important insight into reactivity of OH radical. Again, state-of-the-art ab initio calculations will be employed to determine the shape and depth of the intermolecular potential. This potential can be then used to calculate reaction rates and energy distribution in the products of the reaction.
Vibrational spectroscopy is a well-established method to study structure of wide variety of chemical species. Yet, for molecules containing more than 5 or 6 atoms a quantitative interpretation of measured vibrational spectra (infrared or Raman) is unthinkable without the guidance of computational chemistry. Vast majority of such calculations employ so-called double harmonic approximation. While very convenient, this approximation has some serious drawbacks. We have been testing several approaches that would allow us to overcome shortcomings of harmonic approximation, while being practicable for medium-sized molecules. Wide variety of ab initio and semi-empirically derived potentials will be used in connection with perturbative and variational approaches to solving vibrational problem.
Diazobenzene dyes can exist as cis- (Z) and trans- (E) isomers. These isomers have different geometry, properties, and spectra. Importantly, the isomers can be converted into each other photochemically in a controlled fashion. This opens possibilities for variety of nanotech uses, ranging from holographic data storage to molecular engines. In collaboration with Dr. Morgan, whose group synthesizes these compounds, we investigate the structure, dynamics, and spectroscopy of these compounds. The ultimate goal is to provide a theoretical guidance for synthesis of dyes with specific spectroscopic and/or mechanic properties.