H. Bernhard Schlegel of Wayne State University is supported by an award from the Theoretical and Computational Chemistry program in the Chemistry Division to explore potential energy surfaces for a number of projects, including strong-field chemistry, unimolecular dissociations, and bio-organic chemistry. New computational methods will be developed in areas such as reaction path optimization, automated potential energy surface searching and ab-initio molecular dynamics. Schlegel will continue to pursue advances in time-dependent SCF studies (TDSCF) by incorporating DFT methods and a CIS based approach, developing further technical improvements as well as applications. Ab-initio molecular dynamics (AIMD) investigations will be improved by using bond-additivity corrections, and Schlegel will explore if AIMD can be performed in the presence of a laser field. Improved methods for finding transition states will also be developed, and the use of bond-additivity corrections to improve the accuracy of molecular dynamics simulations will be examined.
This research is wide ranging and affects a variety of scientific disciplines, from physics and materials science to biology. As part of these studies Schlegel will collaborate with various experimental groups, which helps ensure that this work has a broad impact on a wide variety of topics. He has a successful record of training students, not only from his own research group, but also from the groups of his collaborators, to become creative independent scientists. Schlegel freely disseminates the computer codes that he generates for the use of the general research community, including both computational and experimental scientists.
The exploration of reaction pathways and understanding molecular dynamics are key challenges in chemistry. Exploring potential energy surfaces for chemical reactions using electronic structure calculations has been the guiding theme for our research group. Under this broad umbrella, we examined topics in strong field chemistry, ab initio molecular dynamics, potential energy surfaces for bio-organic and inorganic systems, and methods for exploring potential energy surfaces. Strong field chemistry and attosecond science are concerned with short, intense laser pulses interacting with molecular systems and are rapidly growing research areas on the molecular frontier. Attosecond laser pulses can directly explore electron dynamics, image molecular orbitals and probe bond making and breaking processes. Intense laser pulses can act as photonic reagents that can alter the reactivity of molecules. We have used time dependent configuration interaction (TD-CI) to explore the level of theory needed to simulate the response of the electron density to a strong laser fields. The TD-CI approach has then been used to examine the strong field ionization rate of a series of polyenes using a heuristic ionization model. Strong laser fields can alter the potential energy surfaces that determine molecular reactivity. We have used ab initio molecular dynamics (AIMD) to explore the dissociation reactions of monocations, dications and radicals. We have observed non-statistical behavior in branching ratios and changes in dissociation rates induced by strong laser fields. In exploring the potential energy surfaces for bio-organic systems, we have used combined quantum mechanical / molecular mechanical (QM/MM) methods to study the mechanism for KDO synthase (an enzyme important in the synthesis of bacterial cell walls) and the inhibition of matrix metalloproteinase 2 (an enzyme implicated in cancer growth, angiogenesis, metastasis, inflammation and connective tissue diseases). We have also developed a protocol to calculate pKa’s and redox potentials for nucleobases. In collaboration with a number of colleagues at WSU, we have used electronic structure methods to provide an understanding of a number of transition metal complexes with interesting structural and redox properties. These applications of electronic structure calculations drive our continuing efforts to improve methods for finding transition states and reaction paths. Exploring reaction paths and molecular dynamics has a broad impact on understanding chemistry at the molecular level. Strong field chemistry and attosecond science address these challenges by using short intense laser pulses to probe structure and reactivity. We are developing new methods for simulating the behavior of molecules under these extreme conditions. Studying reaction paths for bio-organic systems is equally demanding but the pay-off can be even greater. The selected bio-organic topics that we have investigated are related to infection, toxicity, mutagenesis and cancer.
