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Theoretical chemistry

 

Our group's research interests are in the area of theoretical chemistry. Our focus is twofold: to develop new theoretical methods and implement them in computationally efficient computer programs, and to apply these and other methods to the solution of interesting chemical and spectroscopic problems.

 

Methodology

 

During the 1990s, our group helped to develop so-called equation-of-motion coupled cluster methods that are specifically designed to treat electronically excited states of closed shell (no unpaired electrons) molecules and ground and excited states of radicals. Specifically, we developed methods by which analytic first derivatives of the energy can be calculated at a cost significantly below that needed for numerical differentiation. This advance allows potential energy surfaces of these systems to be studied routinely at a high level of theory, thereby providing information that is needed to properly interpret spectra, reactivity, and molecular dynamics.

In addition, we have worked out and implemented equations for first and second derivatives of the energy for molecules described by the normal coupled-cluster approximation. Among other things, this allows the calculation of NMR chemical shifts at a level of theory that surpasses those available to other research groups at this time. Significantly, our calculations played a prominent role in the positive identification of the N5+ cation, the first all-nitrogen molecule to be discovered in a century.

 

Applications

 

Our group maintains several fruitful collaborations with other theoretical and experimental groups in the US and Europe. Problems presented to us by experimentalists often serve as motivation for the development of new methods and therefore play an important role in shaping our research program. Recently, we have been active in the study of so-called interstellar molecules - those which have been observed or are thought to exist in the interstellar medium. This research comprises applications in two areas: highly accurate calculations of anharmonic molecular force fields, which are almost always needed for a rigorous analysis of microwave spectra; and simulations of electronic spectra, which are currently being used to study the problem of the "diffuse interstellar bands". This is the name given to over two hundred absorption features in the visible region of the spectrum found in diffuse interstellar clouds, only four of which have been assigned to a molecular carrier, and even those assignments are currently under challenge.

 

Representative Publications

 

Y.J. Bomble, J.F. Stanton, M. Kallay and J. Gauss "Coupled-cluster methods including noniterative treatment of quadruple excitations" J. Chem. Phys. 123 (2005): 54101.


E.B. Jochnowitz, M. Nimlos, M.E. Varner, J.F. Stanton and G.B. Ellison "Propargyl radical: Ab initio anharmonic modes and the polarized infrared absorption spectra of matrix isolated HCCCH2" J. Phys. Chem. A109 (2005): 3812.


J.F. Stanton, J.P. Dudek, P. Theule, H. Gupta, M.C. McCarthy and P. Thaddeus "Laser spectroscopy of Si3C" J. Chem. Phys. 123 (2005): 54326.


J. Gauss and J.F. Stanton "Analytic gradients for the coupled-cluster singles, doubles and triples (CCSDT) model" J. Chem. Phys. 116 (2002): 7773.


J.F. Stanton "Coupled-cluster theory, pseudo-Jahn-Teller effects and conical intersections" J. Chem. Phys. 115 (2001): 10382.