Affiliate Professor of Chemistry
Co-Director, Northwest Institute for Advanced Computing
Ph.D. California Institute of Technology, 1970
(Computational and Theoretical Chemistry)
The chemistries of the main group elements in the second and subsequent rows of the Periodic Table (Na–Ar, K–Kr, etc.) often differ dramatically from those of the corresponding first row elements (Li–Ne). Our research is focused on using advanced theoretical methods and computational techniques to characterize the rich chemistry of the main group elements beyond the first row, with a focus on compounds of silicon, phosphorus and sulfur. Our goal is to understand how the electronic structure of these compounds gives rise to the rich chemistry of these elements.
Our research employs electronic structure methods that are capable of yielding highly accurate solutions of the Schrödinger equation—single-reference restricted singles and doubles coupled cluster theory with perturbative triples [CCSD(T), RCCSD(T)], and multireference configuration interaction (MRCI) calculations based on complete active space self-consistent field (CASSCF) wavefunctions with the quadruples correction (+Q). Augmented correlation consistent basis sets of triple and/or quadruple zeta [aug-cc-pV(T,Q)Z] quality, including sets augmented with tight d-functions for the second row atoms, are used to obtain solutions close to the theoretical limit. The predictions from these calculations fill critical gaps in the experimental data available for molecules containing elements from the second row and beyond and provide the basis for a detailed theoretical understanding of the chemistry of these elements.
We complement the accurate calculations described above with generalized valence bond (GVB) calculations. The GVB wavefunction—orbitals and spin couplings—provides detailed insights into the electronic structure and properties of the molecules and reactions being studied. In the GVB wavefunction, the orbitals vary continuously from the atomic or fragment orbitals at large separations to orbitals appropriate for the molecule as the internuclear separation decreases. Similarly, the spin function changes to reflect the coupling of the electrons in the molecule. The GVB wavefunction is more accurate that the HF wavefunction, including non-dynamic correlation effects included in multiconfiguration wavefunctions, such as the Valence Complete Active Space SCF (CASSCF) wavefunction. However, the GVB wavefunction is far more compact and easier to interpret than multiconfiguration wavefunctions.
“Insights into the Perplexing Nature of the Bonding in C2 from Generalized Valence Bond Calculations.” Xu, L.; Dunning, T. H., Jr., J. Chem. Theory Comput. 2014, 10, 195–201.
“The Nature of the SO Bond in Chlorinated Sulfur-Oxygen Compounds.” Lindquist, B. A.; Dunning, T. H., Jr., Theor. Chem. Acc. 2014, 133, 1443.
“Bonding in Sulfur-Oxygen Compounds—HSO/SOH and SOO/OSO: An example of Recoupled Pair π Bonding.” Lindquist, B. A.; Takeshita, T. Y.; Woon, D. E.; Dunning, T. H., Jr., J. Chem. Theory Comput. 2013, 9, 4444–4452.
“Bonding in FSSF3: Breakdown in Bond Length-Strength Correlations and Implications for SF2 Dimerization.” Lindquist, B. A.; Dunning, T. H., Jr., J. Phys. Chem. Lett. 2013, 4, 3139–3143.
“The First Row Anomaly and Recoupled Pair Bonding in the Halides of the Late p-Block Elements.” Dunning, T. H., Jr.; Woon, D. E.; Leiding, J.; Chen, L., Acc. Chem. Res. 2013, 46, 359–368.
“Insights into the Unusual Barrierless Reactions between Two Closed Shell Molecules, (CH3)2S + F2, and Its H2S + F2 Analogue: Role of Recoupled Pair Bonding.” Leiding, J.; Woon, D. E.; Dunning, T. H., Jr., J. Phys. Chem. A 2012, 116, 5247–5255.
“Recoupled Pair Bonding in PFn (n=1-5).” Woon, D. E.; Dunning, T. H., Jr., J. Phys. Chem. A 2010, 114, 8845–8851.
“Bonding in ClFn (n=1-7) Molecules: Further Insight into the Electronic Structure of Hypervalent Molecules and Recoupled Pair Bonds.” Chen, L.; Woon, D. E.; Dunning, T. H., Jr., J. Phys. Chem. A 2009, 113, 12645–12654.
“Theory of Hypervalent Bonding: Recoupled Pair Bonds in SFn (n=1-6).” Woon, D. E.; Dunning, T. H., Jr., J. Phys. Chem. A 2009, 113, 7915–7926.