Welcome to the Stanton Research Group
Welcome to the Stanton Research Group
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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:
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:
Quantum Chemistry
Quantum Chemistry
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.
Spectroscopy
Spectroscopy
Development of model Hamiltonian approaches for the simulation, prediction and non-superficial understanding of electronic spectra
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 CFOUR
Laboratory spectrum of Si3C, 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 Si2C 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 SixCy (x+y=3). All of these molecules are of great astronomical interest, and have interesting electronic structures. Si2C was the last of these to be characterized experimentally.
Bending intervals (E(v=n+1) - E(v=n)) for Si2C, which has a highly anharmonic bending mode with a barrier to linearity of ca. 800 cm-1. This molecule presents a striking example of quantum monodromy (lack of a consistent set of quantum numbers that are 'valid' at different energies), exhibiting qualitatively different level structures below and above the barrier to linearity. The potential is shown schematically in the lower left and is "too scale" (v=6 is below the barrier, v=7 just above it); the energies shown were calculated with various models on an analytic potential surface fit to high-level calculations. The dark curve shows the exact variational results, which are in near perfect agreement with levels measured by dispersed fluorescence of several rovibronic levels near 25000 cm-1.
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, <qa>, which is proportional to the h1 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.
Chemical Kinetics
Chemical Kinetics
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
Above is a plot of the energy distribution in the so-called Criegee intermediate(CH2COO), 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.
Thermochemistry
Thermochemistry
Development of high-accuracy quantum-chemical methods for calculating bond energies, heats of formation, and related properties
Left graphic from Ruscic et al. J. Phys. Chem. A108, 9979 (2004)
Mechanisms of Chemical Reactions
Mechanisms of Chemical Reactions
Kinetics and reaction mechanisms associated with the thermal decomposition of biomass, which are also studied by tunable (synchrotron) photoionization mass spectroscopy and infrared spectroscopy
Schematic potential energy surface governing isomers of CH2O2 as well as the related dissociation products. The celebrated Criegee intermediate is the least stable minimum energy structure on this potential surface, and is seen at the upper left.
Energies (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.
Events & News
Events & News
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.
Software and Related Projects
Software and Related Projects
Together 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.
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, that of Prof. G. Barney Ellison at the University of Colorado, that of Joshua Baraban at Ben Gurion University in Israel, and P. Bryan Changala at the Harvard-Smithsonian Center for Astrophysics.
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.
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