Luciano N. Vidal

Cálculo ab initio de intensidades Raman dinâmicas utilizando a teoria da resposta linear

In this paper a methodology for the computation of Raman scattering cross-sections and depolarization ratios within the Placzek Polarizability Theory is described. The polarizability gradients are derived from the values of the dynamic polarizabilities computed at the excitation frequencies using ab initio Linear Response Theory. A sample application of the computational program, at the HF, MP2 and CCSD levels of theory, is presented for H2O and NH3. The results show that high correlated levels of theory are needed to achieve good agreement with experimental data.

Implementação computacional do modelo carga-fluxo de carga-fluxo de dipolo para cálculo e interpretação das intensidades do espectro infravermelho

The first computational implementation that automates the procedures involved in the calculation of infrared intensities using the charge-charge flux-dipole flux model is presented. The atomic charges and dipoles from the Quantum Theory of Atoms in Molecules (QTAIM) model was programmed for Morphy98, Gaussian98 and Gaussian03 programs outputs, but for the ChelpG parameters only the Gaussian programs are supported. Results of illustrative but new calculations for the water, ammonia and methane molecules at the MP2/6-311++G(3d,3p) theoretical level, using the ChelpG and QTAIM/Morphy charges and dipoles are presented. These results showed excellent agreement with analytical results obtained directly at the MP2/6-311++G(3d,3p) level of theory.

Core–valence correlation effects on IR calculations: the BF3 and BCl3 cases

The first theoretical results of core–valence correlation effects are presented for the infrared wavenumbers and intensities of the BF3 and BCl3 molecules, using (double– and triple–zeta) Dunning core–valence basis sets at the CCSD(T) level. The results are compared with those calculated in the frozen core approximation with standard Dunning basis sets at the same correlation level and with the experimental values. The general conclusion is that the effect of core–valence correlation is, for infrared wavenumbers and intensities, smaller than the effect of adding augmented diffuse functions to the basis set, e.g., cc–pVTZ to aug–cc–pVTZ. Moreover, the trends observed in the data are mainly related to the augmented functions rather than the core–valence functions added to the basis set. The results obtained here confirm previous studies pointing out the large descrepancy between the theoretical and experimental intensities of the stretching mode for BCl3.