Cálculos de propiedades moleculares con métodos de correlación electrónica extensivos.

Résumé

In this work, PROP software for the calculation of electronic properties as mean value from CI vectors obtained with the CASDI code has been developed. This software allows the use of (SC)2-CI expansions over SDCI. One of the objectives of the work was to state the reliability of the (SC)2 method for the calculation of molecular electronic properties. The present work has focused, for the first time, in a systematic study of electronic properties calculations using (SC)2 expansions. single reference and multireference wavefunctions. The values calculated with (SC)2CI expansions are closer to the reference values than those obtained with the corresponding bare undressed- SDCI wavefunctions. This behaviour had been well established in the past for the energy. The electronic properties obtained employing the (SC)2 dressing method are size-consistent if the proceeding shown is employed to obtain them. The aug-cc-pVTZ basis set is the optimum basis set for the calculation of accurate electronic properties employing the (SC)2 dressing method in molecules containing atoms of the first rows of the periodic table. It is advisable to include a second set of augmented functions in the basis set, whenever it is possible. Those basis sets grant the best accuracy/computational-cost ratio As a general behaviour, the improvement in the properties calculated using the (SC)2 dressing method over the ones obtained using the bare SR-SDCI wavefunction is greater than the improvement observed when a undressed MR-SDCI wavefunction is employed, being the computational effort much lesser in the first case. New theoretical reference values for correlation methods have been obtained during the high-detail FCI study of Be3 molecule Finally, the presented methodology has been successfully applied to the study of real problems. In the corresponding calculations, rovibrational and temperature related terms have been taken into account