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Author Glowacki, David R. ♦ Orr-Ewing, Andrew J. ♦ Harvey, Jeremy N.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY ♦ CARBON NITRIDES ♦ CHEMICAL BONDS ♦ COUPLING ♦ DEUTERIUM COMPOUNDS ♦ ENERGY ABSORPTION ♦ ENERGY LOSSES ♦ EQUILIBRIUM ♦ FLUORINE ♦ MATHEMATICAL SOLUTIONS ♦ MOLECULAR DYNAMICS METHOD ♦ MOLECULES ♦ POTENTIAL ENERGY ♦ RED SHIFT ♦ RELAXATION ♦ SOLUTES ♦ SOLVATION ♦ SOLVENTS ♦ SPECTRAL SHIFT ♦ TIME DEPENDENCE ♦ VALENCE
Abstract We describe a parallelized linear-scaling computational framework developed to implement arbitrarily large multi-state empirical valence bond (MS-EVB) calculations within CHARMM and TINKER. Forces are obtained using the Hellmann-Feynman relationship, giving continuous gradients, and good energy conservation. Utilizing multi-dimensional Gaussian coupling elements fit to explicitly correlated coupled cluster theory, we built a 64-state MS-EVB model designed to study the F + CD{sub 3}CN → DF + CD{sub 2}CN reaction in CD{sub 3}CN solvent (recently reported in Dunning et al. [Science 347(6221), 530 (2015)]). This approach allows us to build a reactive potential energy surface whose balanced accuracy and efficiency considerably surpass what we could achieve otherwise. We ran molecular dynamics simulations to examine a range of observables which follow in the wake of the reactive event: energy deposition in the nascent reaction products, vibrational relaxation rates of excited DF in CD{sub 3}CN solvent, equilibrium power spectra of DF in CD{sub 3}CN, and time dependent spectral shifts associated with relaxation of the nascent DF. Many of our results are in good agreement with time-resolved experimental observations, providing evidence for the accuracy of our MS-EVB framework in treating both the solute and solute/solvent interactions. The simulations provide additional insight into the dynamics at sub-picosecond time scales that are difficult to resolve experimentally. In particular, the simulations show that (immediately following deuterium abstraction) the nascent DF finds itself in a non-equilibrium regime in two different respects: (1) it is highly vibrationally excited, with ∼23 kcal mol{sup −1} localized in the stretch and (2) its post-reaction solvation environment, in which it is not yet hydrogen-bonded to CD{sub 3}CN solvent molecules, is intermediate between the non-interacting gas-phase limit and the solution-phase equilibrium limit. Vibrational relaxation of the nascent DF results in a spectral blue shift, while relaxation of the post-reaction solvation environment results in a red shift. These two competing effects mean that the post-reaction relaxation profile is distinct from what is observed when Franck-Condon vibrational excitation of DF occurs within a microsolvation environment initially at equilibrium. Our conclusions, along with the theoretical and parallel software framework presented in this paper, should be more broadly applicable to a range of complex reactive systems.
ISSN 00219606
Educational Use Research
Learning Resource Type Article
Publisher Date 2015-07-28
Publisher Place United States
Journal Journal of Chemical Physics
Volume Number 143
Issue Number 4


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