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Structure Dependence of Hyperpolarizability in Octopolar Molecules
Cardoso, C.; Abreu, P. E.; Nogueira, F.Recent Hyper Rayleigh Scattering measurements report a significant increase of second-order hyperpolarizability upon introduction of positive charges at the pyridyl end groups in trispyridyl octopolar chromophores. We calculated the geometries, linear response, and first-order hyperpolarizabilities of a series of six trispyridyl molecules both in the neutral and protonated forms. The calculations were performed...
Comparison of the climatic conditions and tomato crop productivity in Mediterra...
Baptista, F.J.; Abreu, P.E; Meneses, J.F.; Bailey, B.J.This study was based on experiments with a tomato crop, carried out in two Mediterranean unheated greenhouses, located at the Instituto Superior of Agronomia, Lisbon. The main objective was to compare the behaviour of internal air parameters such as air temperature and relative humidity and the likelihood of condensation on the greenhouse cover in two greenhouses with different management of natural ventilation...
MRCI Calculation, Scaling of the External Correlation, and Modeling of Potentia...
Peña-Gallego, A.; Abreu, P. E.; Varandas, A. J. C.The first lowest 2Π and 2Σ+ states of OCl, as well as the 1Σ+ and 3Σ+ states of HCl, have been calculated at the ab initio MRCI level, and modeled semiempirically using the extended Hartree−Fock approximate correlation energy method. Spectroscopic RKR data and accurate ab initio energies have been used to obtain the model parameters. The vibrational levels of those states have also been calculated, and found to...
First principles calculation of the potential energy surface for the lowest-qua...
Abreu, P. E.; Varandas, A. J. C.We report a study of the potential energy surface for the lowest quartet state of H3. At the ab initio level, restricted Hartree–Fock and full configuration interaction (FCI) calculations were performed with two extended Gaussian basis sets providing a detailed coverage of the molecule configuration space. A total of 102 geometries, both linear and nonlinear, have been examined. These calculated energies have t...
Quasi-ab initio dynamics: a test trajectory study of the reaction using energi...
Varandas, A. J. C.; Abreu, P. E.We have carried out a test dynamics study of the prototype exchange reaction by running quasi-classical trajectories [`]on-the-fly' using ab initio correlated energies which have been previously corrected semiempirically by the double many-body expansion plus scaling of the external correlation method to account for size-limitations of the one-electron basis set and configuration interaction expansion. The meth...
Toward a Single-Valued DMBE Potential Energy Surface for CHNO(3A). 1. Diatomic ...
Jimeno, P.; Rayez, J. C.; Abreu, P. E.; Varandas, A. J. C.As a first step toward the construction of a single-valued double many-body expansion potential energy surface for CHNO(3A), we have carried out CASSCF and CASPT2 calculations of six diatomic curves, involving a total of nine electronic states. The ab initio curves have been represented analytically using the extended Hartree−Fock approximate correlation energy model. In all cases, the semiempirical curves have...
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