We are a research group in theoretical chemical physics, particularly the area known as quantum chemistry and its application to problems in molecular spectroscopy, thermochemistry and chemical kinetics. Amongst the topics of research currently being pursued in our group are the following: Development, and extensions, of the equation-of-motion coupled-cluster method Quasidiabatic approaches in coupled-cluster theory Improvement of algorithms for existing high-level quantum-chemical methods Methods for calculating cross-sections for photoelectron spectra "Magic square" determining ideal strategy for permutations of four-index quantities (quadruple excitation amplitudes and increments to same) for use in solving the CCSDTQ equations. A very efficient implementation of CCSDTQ and CCSDT(Q) is a part of the new release of CFOUR.SpectroscopyLaboratory spectrum of Si_{3}C, recorded at the Harvard-Smithsonian for Astrophysics by N.J. Reilly, D.L. Kokkin and M.C. McCarthy (black), together with simulation based on EOM-CCSDT calculations. The Si_{2}C molecule was recently discovered to be abundant in the interstellar medium, the first molecule known in space to contain two copies of the very abundant silicon atom. The discovery was built upon laboratory work of M.C. McCarthy and associates at Harvard University, which was done with the assistance of theoretical calculations done by our group. The equilibrium structure of Si2C is shown in the figure as well as the family of molecules Si_{x}C_{y} (x+y=3). All of these molecules are of great astronomical interest, and have interesting electronic structures. Si_{2}C was the last of these to be characterized experimentally.
Properties of stationary states for model system exhibiting E x e linear Jahn-Teller coupling. The plots are probability densities, where the horizontal axis corresponds to the totally symmetric component of the degenerate mode and the vertical axis to the nonsymmetric component. The origin is at the center, and the range of coordinates is -5 < q < 5, where q is a dimensionless normal coordinate. The central column gives the expectation value of the totally symmetric part of q, <q_{a}>, which is proportional to the h_{1} Jahn-Teller parameter. The latter is currently the focus of a project that we are working on with the Terry Miller group at Ohio State University (although we are Michigan fans). All data here is produced by the xsim program, which is a product of our research group.Investigation of the interesting physics and mathematics that are encountered in the presence of degeneracies, including, but not limited to the Jahn-Teller effect Breakdowns of the Born-Oppenheimer model as manifested in molecular spectroscopy Ongoing development of the xguinea and xsim spectral simulation packages, which are now a part of CFOURChemical KineticsAbove is a plot of the energy distribution in the so-called Criegee intermediate(CH_{2}COO), immediately after it is formed from the bimolecular reaction of ethylene and ozone. The temperature and temperature of the reaction are taken to be 300 K and 1 atm, roughly simulating ambient atmospheric conditions, and <J> = 40.The use and efficient implementation of semiclassical transition state theory (SCTST), which is a non-empirical theory that accounts for effects such as tunneling and path anharmonicity Development of models for the calculation of chemical kinetics, including the two-dimensional (pressure and temperature) master equation Application studies of reactions that occur in combustion processes, and those relevant to the chemistry of the atmosphere. ThermochemistryLeft graphic from Ruscic et al. J. Phys. Chem. A108, 9979 (2004)Development of high-accuracy quantum-chemical methods for calculating bond energies, heats of formation, and related properites. Mechanisms of Chemical ReactionsEnergies (in kJ mol^{-1}, relative to separated HO and CO) of relevant points on the HOCO potential energy surface, with activation energies given in italics. Apart from the pathway leading to the cis isomer of the title molecule, all values are HEAT-345(Q) calculations. The formation of HOCO from HO+CO passes through a linear (OHCO) pre-reactive complex which then leads to a trans transition state with the energy given in the lower right quadrant of the figure. The energy given above for the {\it cis} pathway is that of the {\it trans} transition state plus the FC-CCSD(T)/ANO1 energy difference between it and the corresponding cis conformer, which is a second-order saddle point. | JT2020: The 25th biannual international symposium devoted to the Jahn-Teller Effect, will be held June 13-16, 2020 in beautiful Telluride Colorado. Details of the meeting can be found here for those of you that might wish to attend. Two-dimensional mass spectrum of cyclohexanone, obtained by Jessie Porterfield, Oleg Kostko, Musa Ahmed and Barney Ellison using synchrotron radiation at the Advanced Light Source (Lawrence Berkeley National Laboratory) in the Autumn of 2014. The two axes are m/z (x axis) and photon energy (y axis, in eV). The peak at m/z=98 is due to the parent species; the appearance of other masses at energies above 10.5 eV is due to dissociative ionization via cyclohexanone+ or its (more stable) enol+ isomer.SOFTWARETogether with the groups of J. Gauss (Mainz, Germany) and P.G. Szalay (Budapest, Hungary), we develop the CFOUR quantum chemistry package, which is freely distributed to all interested parties. For more information about CFOUR, see: www.cfour.de A new release of CFOUR should happen no later than spring 2018 We are involved in the Scalable High-Performance Computing Group, which is headed by Prof. Robert van de Geijn in the computer science department at UT-Austin. For more information, look here. Another community effort of our research group is the MultiWell program suite for chemical kinetics calculations, a project that is headed by Prof. John Barker of the Department of Climate and Space Sciences and Engineering at the University of Michigan in the great city of Ann Arbor. For more information,go here and have a read. A chemical kinetics discussion group has also been formed, and can be found here. We are privileged to be a part of the Active Thermochemical Tables project, a revolutionary advance in thermochemistry developed by Branko Ruscic at Argonne National Laboratory. The development of ATcT has had a profound impact on thermochemistry; the enthalpies of formation for several key molecular species are now known much more precisely than they were a decade ago, with reduction of error bars typically by an order of magnitude. By providing accurate and precise information about the thermodynamic stability of molecules, ATcT will have profound impact on the fidelity of modeling studies. The current ATcT team consists of Ruscic and his group at ANL, our team, and that of Prof. G. Barney Ellison at the University of Colorado. |