Advances in Coupled-Cluster Theory with Molecular Applications

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John Stanton of the University of Texas Austin is supported by an award from the Theory, Models and Computational Methods program in the Chemistry division to develop new computational and theoretical approaches based on coupled-cluster theory that are aimed at specific applications. The award is co-funded by a pilot program in OCI promoting the reuse of Cyberinfrastructure (CI) elements. The Stanton group is developing methods to treat radicals and biradicals, developing (quasi)diabatic representations for interacting systems, improving the implementation of other high-accuracy coupled-cluster techniques and extending their ability to describe the spectra of strongly interacting systems to include molecules for which a low-order polynomial representation of the potential is inadequate. Applications include spectroscopically interesting problems such as the nitrate radical and high-resolution electronic and photoelectron spectra of radicals and transient intermediates. An additional application is a project aimed at determining molecular mechanisms of thermal degradation of prototype biomass molecules. Much of the application work is done in collaboration with leading experimental groups in the United States. The theoretical method development performed by the Stanton group is ultimately included in the computational package cfour1 which is distributed free of charge. The tools that the Stanton group develops for analyzing molecular spectra are aimed at a broad group of researchers, particularly experimentalists who are not experts in computational chemistry. The research funded under this program is extending the usefulness of these codes to a wider group of scientists. Undergraduates are very involved in this research program.