Washington B. da Silva

Trial wave functions for the calculation of vibrational states of molecules using quantum Monte Carlo

In this article we test three kinds of trial wave functions for the calculation of vibrational excited states of molecules using quantum Monte Carlo. We begin our study with the basis set originally used by Bernu and co-workers and further modified by Acioli and Soares Neto. The second set tested was the simplified Morse oscillator-like with harmonic coupling (SMOL-HC) proposed by Brown et al. to study the vibrational spectra of C3. Finally we proposed a third basis set, based on the previous two. This basis set keeps the anharmonicity of the SMOL-HC basis but with well conditioned Hamiltonian and overlap matrices. The calculations were performed in the H2, H3+, and H2O molecules. The results indicate that the basis sets proposed in this work yield more accurate results with a smaller number of basis functions.

Theoretical study of the H + HCN → H + HNC process

AbstractWe present a theoretical study on the detailed mechanism and kinetics of the H+HCN →H+HNC process. The potential energy surface was calculated at the complete basis set quantum chemical method, CBS-QB3. The vibrational frequencies and geometries for four isomers (H2CN, cis-HCNH, trans-HCNH, CNH2), and seven saddle points (TSn where n = 1 − 7) are very important and must be considered during the process of formation of the HNC in the reaction were calculated at the B3LYP/6-311G(2d,d,p) level, within CBS-QB3 method. Three different pathways (PW1, PW2, and PW3) were analyzed and the results from the potential energy surface calculations were used to solve the master equation. The results were employed to calculate the thermal rate constant and pathways branching ratio of the title reaction over the temperature range of 300 up to 3000 K. The rate constants for reaction H + HCN → H + HNC were fitted by the modified Arrhenius expressions. Our calculations indicate that the formation of the HNC preferentially occurs via formation of cis–HCNH, the fitted expression is kPW2(T) = 9.98 × 10−22T2.41 exp(−7.62 kcal.mol−1/RT) while the predicted overall rate constant kOverall(T) = 9.45 × 10−21T2.15 exp(−8.56 kcal.mol−1/RT) in cm3 molecule−1s−1. Graphical Abstract(a) Potential energy surface, (b) thermal rate constants as a function of temperature and (c) the branching ratios (%) of PW1, PW2, PW3 pathways involved in rm H + HCN → H + HNC process.

Previsão de Novos Canais de Reação para o CN + C2H2

Neste trabalho, apresentamos um estudo da reacao do ciano (CN) com a molecula C 2 H 2 . Mais precisamente, determinamos as geometrias, frequencias e energias eletronicas para as diferentes especies envolvidas nos caminhos de reacao do processo CN + C 2 H 2 usando o nivel de calculo M06L/ 6-311++G(d,p). A partir deste estudo, foi possivel propor tres novos caminhos de reacao para este importante processo colisional. DOI: 10.5935/1984-6835.20160038

Kinetic Mechanism Study of Reaction C2H + C2H2via TST

In this work, we present the Potential Energy Surface – PES of the reaction of C2H with C2H2 molecule. More precisely, we determined the geometries, frequencies, and electronic energies for the species involved in the C2H+C2H2 reaction pathways at the B3LYP/6-311++G(d,p) and CBS-QB3 levels. From this study, we calculated the Rate Constant for two pathways of the reaction via Transition State Theory TST. The reaction proceeds in two steps and rate constants were calculated for the temperature

Predicting New Pathways for the Reaction CN + C2H2

In this work, we present a study of the reaction of cyano (CN) with C2H2 molecule. More precisely, we determined the geometries, frequencies, and electronic energies for the various species involved in the CN+C2H2 reaction pathways at the M06L/6311++G(d,p) level. From this study, it was possible to propose three new pathways for this important reactive scattering process.