QUANTUM CHEMISTRY, REACTION DYNAMICS, AND INTERMOLECULAR FORCES

Piotr Piecuch Assistant Professor (b. 1960). M.Sc., 1983, University of Wroclaw (Poland); Ph.D., 1988, University of Wroclaw (Poland); Postdoctoral Fellow, 1988-91, University of Waterloo (Canada); Adjunct, 1990-92, University of Wroclaw (Poland); Postdoctoral Research Associate, 1992-93, University of Arizona; Visiting Assistant Professor, 1994-95, University of Waterloo (Canada); Visiting Assistant Professor, 1995-97, University of Toronto (Canada); Postdoctoral Research Associate, 1997-98, University of Florida. Theoretical and Computational Chemistry. New quantum-chemical methods. Applications of ab initio quantum mechanics to molecular electronic structure, properties, spectroscopy, and reaction dynamics. Theory of weak interactions between atoms and molecules. 517-355-9715, Ext. 223 piecuch@cem.msu.edu

My research focuses on (i) ab initio quantum theory of molecular electronic structure, (ii) molecular properties and spectroscopy, (iii) reaction dynamics, and (iv) theory of intermolecular forces. The aim is to design and apply quantum-mechanical methods that enable precise determination of potential energy surfaces and property functions (e.g., dipole moment function) for both existing and hypothetical molecular systems in their ground and excited states as well as calculations of intermolecular potentials for van der Waals complexes.

Quantum theory of molecular electronic structure. The key to understanding molecular electronic structure and dynamic behavior of molecules is an accurate assessment of electron correlation effects. Our group will focus on new quantum-chemical methods that include correlation, particularly on the coupled-cluster theory and its multi-reference and response generalizations that allow us to study electronically excited states, bond breaking, electron attachment processes, molecular properties in vibrationally and electronically excited states, and transition probability coefficients for various types of spectroscopy. Our primary interest is in high-accuracy methods that allow us to be predictive, so that we can provide ongoing experiments with new insights and study reaction intermediates and hypothetical species in the absence of experiment.

Molecular properties and spectroscopy. We will use our linear-response coupled-cluster methods along with other ab initio approaches, such as multi-reference configuration interaction method, to calculate molecular electric multipole moments and (hyper)polarizabilities and the effect of nuclear motion on these properties. We will use first-principles theories to obtain rovibrational and electronic spectra of molecules, including systems of astrophysical interest and van der Waals complexes that are precursors of photoinduced charge-transfer reactions.

Reaction dynamics. We will study the photoinduced charge-transfer ("harpooning") reactions between alkali and alkaline earth metal atoms and halides using state-of-the-art ab initio and dynamical methods. These electronically non-adiabatic reactions are studied experimentally by the leading research groups, including Professor Polanyi's group at the University of Toronto. Collaboration with Professor Polanyi's group will give us an opportunity to test our theoretical models and, at the same time, to contribute to a rapidly growing field of "transition state spectroscopy". We will also study the kinetics of elementary reactions pertinent to combustion and atmospheric chemistry. Again, we will rely on ab initio potential energy surfaces and properties.

Theory of intermolecular forces. Intermolecular potentials are a necessary ingredient for the determination of the structure, stability, and dynamics of weakly bound clusters and condensed phases. Our group will focus on pairwise non-additive interactions which are important when three or more atoms or molecules interact. We will study trimers and tetramers involving noble gas atoms and small molecules that have been studied experimentally. Interactions in dimers will be studied as well. We will use state-of-the-art quantum chemistry, including methods developed in our group, to generate the necessary information about interacting species.

Representative Publications

The Photoabsorption Spectrum of the Na···FH van der Waals Molecule. Comparison of Theory and Experiment for a Harpooning Reaction Studied by Transition State Spectroscopy, M. S. Topaler, D. G. Truhlar, X. Y. Chang, P. Piecuch, and J. C. Polanyi, J. Chem. Phys., 108, 5378 (1998).

An Ab Initio Determination of ¹A₁— ³B₁ Energy Gap in CH₂ Using Orthogonally Spin-Adapted State-Universal and State-Specific Coupled-Cluster Methods, P. Piecuch, X. Li, and J. Paldus, Chem. Phys. Lett., 230, 377 (1994).

Towards Classification and Analytical Description of Molecular Interactions Including Quantum-Mechanical Many-Body Effects, P. Piecuch, Molecules in Physics, Chemistry and Biology, ed. J. Maruani (Kluwer, Dordrecht, 1988), Vol. 2, p. 417.

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