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Applications of Quantum Chemistry to Chemical Structure and Reactivity

Thomas C. Allison      Research Opportunity Number 50.63.21.B7728

A wide variety of projects are available for study. The central themes of these projects are (1) validation of quantum chemistry methods, (2) interpretation of experimental spectra, (3) development of semi-empirical methods, (4) studies of reactivity indices, (5) computational electrochemistry, and (6) chemical informatics.

The explosion in popularity of density functional theory (DFT) has created an opportunity for critical evaluation of the performance of DFT methods versus accurate quantum and experimental data. Quantities such as HOMO-LUMO gaps and reaction barriers (transition states) are among the well-known cases where DFT methods often come up short. Careful validation studies will establish what functionals yield the most accurate results and reveal systematic deficiencies. Such studies open the door to the development of improved functionals.

Quantum chemistry continues to show its value in supporting and interpreting experimental spectroscopic data. A close cooperation between theoretical calculations and experiments has yielded a number of opportunities for quantum chemistry calculations to clearly identify species found in spectra and to suggest new avenues for experimental study.

As the number of atoms in a molecule increases, calculations become correspondingly expensive. One means of addressing this problem is through the development and parameterization of semi-empirical methods. A tight binding code has been developed in our division and in collaboration with other researchers. Tight binding methods have proven to yield reliable results on larger molecular systems with suitable parameterization. We are studying ways to automate parameter generation to facilitate further studies. Applications of the tight binding methodology include (but are not limited to) biomolecules, transition metal surfaces, and nanoparticles.

Chemical Reactivity Theory provides a framework for the calculation of a number of indices which characterize chemical reactivity (e.g., Fukui function, electrophilicity). These indices can be correlated to reactive sites with a molecule and can be used to predict rates of chemical reactions. We are applying these methodologies in such diverse areas as the calculation of global warming potentials and of rates of chemical reactions on nanoparticle surfaces.

Simulation of reactive processes on metallic surfaces and on the surfaces of metallic nanoparticles in an aqueous environment and with potential control (electrochemistry) is an extremely challenging problem at the forefront of computational chemistry. We are beginning to move into this new field in collaboration with an experimental electrochemistry group. Among the many application areas are clear energy generation and storage.

One of the signature data products in our division is the NIST Chemistry WebBook. We seek to expand the coverage and quality of the WebBook by contributing our research to this database whenever appropriate. As a byproduct of this work, there are a number of opportunities to apply cheminformatics tools and techniques to the data set. This activity produces opportunities for extended validation studies and for new discovery through mining of the database.

Our group has access to a number of computational resources including locally managed and centrally managed Linux clusters, as well as computer time grants from national research facilities. We routinely use codes such as NWChem, GAMESS, Gaussian, MolPro, WIEN2k, OpenMX, and MOPAC, as well as codes developed within our group.


References

Li Y, et al: Journal of the American Chemical Society 134: 1990, 2012

Allison TC, Tong YYJ: Physical Chemistry Chemical Physics 13: 12858, 201