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Ma D.,Max Planck Institute for Solid State Research | Li Manni G.,Max Planck Institute for Solid State Research | Olsen J.,University of Aarhus | Gagliardi L.,Supercomputing Institute | Gagliardi L.,University of Minnesota
Journal of Chemical Theory and Computation

A multireference second-order perturbation theory approach based on the generalized active space self-consistent-field (GASSCF) wave function is presented. Compared with the complete active space (CAS) and restricted active space (RAS) wave functions, GAS wave functions are more flexible and can employ larger active spaces and/or different truncations of the configuration interaction expansion. With GASSCF, one can explore chemical systems that are not affordable with either CASSCF or RASSCF. Perturbation theory to second order on top of GAS wave functions (GASPT2) has been implemented to recover the remaining electron correlation. The method has been benchmarked by computing the chromium dimer ground-state potential energy curve. These calculations show that GASPT2 gives results similar to CASPT2 even with a configuration interaction expansion much smaller than the corresponding CAS expansion. © 2016 American Chemical Society. Source

Truhlar D.G.,Supercomputing Institute
Journal of Physical Organic Chemistry

This paper is a response to an invitation to share my viewpoint by writing an opinion piece (not a review) on proton tunneling, especially from the point of view of whether it has a greater importance in enzymatic reactions than in other reactions. The paper begins with a discussion of the emergence of a conceptual framework for including tunneling in reaction rate calculations; the framework is general enough to include not only transfer of protons but also transfer of hydrogen atoms and hydride ions and their isotopes, and not only enzymatically catalyzed reactions but also nonenzymatic reactions. Then the paper discusses the special issues that arise when the reaction rate under consideration is for an enzyme-catalyzed reaction. The emphasis is on physical considerations in reaction rate calculations, not on system-specific comparison of results for different modes of reaction. It is argued that enzymatic and nonenzymatic reactions may be treated within the same basic framework except that ensemble averaging, which is not usually required for gas-phase reactions, is essential for treating enzyme reactions. Enzymes explicitly discussed include methylamine dehydrogenase, aromatic amine dehydrogenase, E. coli dihydrofolate reductase, hyperthermophilic dihydrofolate reductase, liver alcohol dehydrogenase, methylmalonyl-CoA mutase, soybean lipoxygenase, copper amine oxidase, pentaerythritol tetranitrate reductase, morphinone reductase, enolase, xylose isomerase, and 4-oxalocrotonate tautomerase. Copyright © 2010 John Wiley & Sons, Ltd. Source

Averkiev B.B.,Supercomputing Institute | Truhlar D.G.,Supercomputing Institute
Catalysis Science and Technology

The Gibbs energy of reaction of oxidative addition of ammonia to an iridium complex in diethyl ether was calculated by seven density functional methods, in particular B3LYP, PBE, CAM-B3LYP, M05, M06, M06-L, and ωB97X. The calculated free energies, based on geometry optimization and frequency calculations in both the gas phase and solution, were compared with the experimental result, -1.3 kcal mol-1, obtained by Hartwig and coworkers. The M06-L method gives the best result: -1.4 kcal/mol. © 2011 The Royal Society of Chemistry. Source

Winikoff S.G.,Supercomputing Institute | Cramer C.J.,Supercomputing Institute
Catalysis Science and Technology

We characterize a mechanism for a monomeric copper catalyst reported to oxidize water in bicarbonate solution when subject to sufficiently high external potentials at near neutral pH values. Density functional computations establish the thermochemical equilibria associated with microscopic redox and proton transfer steps and further reveal that O-O bond formation is associated with the unusual reaction of a coordinated hydroxide and carbonate ligand to generate a peroxycarbonate intermediate. The peroxycarbonate complex then decomposes through a retrocyclization to liberate O2 and CO2 and ultimately complete the catalytic cycle. © 2014 the Partner Organisations. Source

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