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Drozd G.T.,Carnegie Mellon University | Melnichuk A.,Quantum Theory Project | Donahue N.M.,Carnegie Mellon University
Journal of Chemical Physics | Year: 2010

The absorption cross section of HOOH, a starting point for larger ROOH, was calculated using the "Wigner method." Calculations use the Wigner transform of ground state wave functions and classical approximations for excited state wave functions. Potential energy and transition dipole moment surfaces were calculated using the equation-of-motion coupled-cluster singles and doubles method over an extended Franck-Condon region. The first two O-O stretches and the first five HOOH torsional levels are included. This study also addresses two fundamental questions about ROOH photodissociation. The long wavelength à 1 A: B̃ 1 B excited state preference has been measured from dynamics experiments, but a Franck-Condon overlap explanation has not been directly verified. A moderate barrier to HOOH torsional motion and excited state dynamics affect the temperature dependence in the UV spectrum. Based on these initial findings for HOOH, photodissociation of large ROOH cannot be eliminated as an important factor for ozone and particulate matter production seen in both ambient and laboratory studies. © 2010 American Institute of Physics.

Cheng H.-P.,Quantum Theory Project
Molecular Physics | Year: 2010

In this paper, a few problems based on my work at QTP are selected and organized with a focus on physical systems and processes that involve interaction between extended states in solids and localized states in molecules. Such interactions are ubiquitous in interfacial processes that stir an intense interest in the science community. © 2010 Taylor & Francis.

Claudino D.,Quantum Theory Project | Gargano R.,University of Brasilia | Carvalho-Silva V.H.,State University of Goias | E Silva G.M.,University of Brasilia | And 2 more authors.
Journal of Physical Chemistry A | Year: 2016

The present paper concludes our series of kinetics studies on the reactions involved in the complex mechanism of nitrogen trifluoride decomposition. Two other related reactions that, along with this mechanism, take part in an efficient boron nitride growth process are also investigated. We report results concerning two abstraction reactions, namely NF2 + N ⇄ 2NF and NF3 + NF ⇄ 2NF2, and two dissociations, N2F4 ⇄ 2NF2 and N2F3 ⇄ NF2 + NF. State-of-the-art electronic structure calculations at the CCSD(T)/cc-pVTZ level of theory were considered to determine geometries and frequencies of reactants, products, and transition states. Extrapolation of the energies to the complete basis set limit was used to obtain energies of all the species. We applied transition state theory to compute thermal rate constants including Wigner, Eckart, Bell, and deformed theory corrections in order to take tunneling effects into account. The obtained results are in good agreement with the experimental data available in the literature and are expected to provide a better phenomenological understanding of the NF3 decomposition role in the boron nitride growth for a wide range of temperature values. © 2016 American Chemical Society.

Wu Y.-N.,Quantum Theory Project | Kebaili N.,University Paris - Sud | Cheng H.-P.,Quantum Theory Project | Cahuzac P.,University Paris - Sud | And 2 more authors.
Journal of Chemical Physics | Year: 2012

To understand the role of chlorine in the stability and the observed fragmentation of Ag dendritic nanostructures, we have studied computationally two model systems using density functional theory. The first one relates to diffusion of Ag n and Ag n Cl m (n 1-4) clusters on an Ag (111) surface, and the second demonstrates interaction strength of (Ag 55)2 dimers with and without chloridation. Based on our calculated energy barriers, Ag n Cl m clusters are more mobile than Ag n clusters for n 1-4. The binding energy between two Ag 55 clusters is significantly reduced by surface chloridation. Bond weakening and enhanced mobility are two important mechanisms underlying corrosion and fragmentation processes. © 2012 American Institute of Physics.

Gregusova A.,Quantum Theory Project | Perera S.A.,Quantum Theory Project | Bartlett R.J.,Quantum Theory Project
Journal of Chemical Theory and Computation | Year: 2010

Benchmark CCSD(T) 15N NMR calculations are performed for 35 experimentally known 15N shifts of 29 molecules. For the eight known gas phase experimental values of N2, HCN, CH3CN, NNO, NH3, NNO, (CH3)3N, and CH3NH 2, CCSD(T) with a basis set previously calibrated for 13C shifts is accurate to 0.2-3 ppm except for the NNO shift, which shows a deviation of 6 ppm. However, the differences between the computed and experimental values in solution due to solvent and finite temperature effects can be as large as ∼25 ppm and must be estimated to relate gas phase 0 K computed values to experiment. An empirical correction is obtained by studying the variations between the estimated solvent effects and the absolute shielding constant. It is shown that the average deviation of computed shifts falls to 3.6 ppm from 12.6 ppm when the correction is applied. © 2010 American Chemical Society.

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