Automatização do uso de simetria no programa PLACZEK, desenvolvido para cálculos dos espectros infravermelho e Raman

Abstract

Since its creation, in 19th century, through present days, the Theory of Group have been applied with huge success in severel areas of science like spectroscopy and quantum chemistry. Our research group, particularly, has developed a software (PLACZEK) for infrared and Raman spectra calculations that uses knowledge of point groups to predict and to label actives transitions and also as a computational tool that allows to reduce the CPU time necessary for the calculation of theses spectra. This work presents a metodology developed to automate the use of symmetry in PLACZEK’s program, specially concerning the classification of normal modes of vibration in the symmetry species of molecular point group and also in the prediction of actives transitions. The exploration of symmetry requires the use of character tables of point group of the molecule. The character tables have a symmetry operations set – e.g, a rotation around an axis – and each of these have its symmetry element, that can be a point, a line or a plane. The spacial orientation of these elements is determined by the character tables and the molecule needs to be spacially oriented in a way that its symmetry elements coincide the one of the table. This requirement makes the preparation of PLACZEK’s program input be tedius, because the user should reorient the molecule in order to take into account the character tables’ requirement. The metodology here described eliminates this step, transferring to PLACZEK’s program the problem of molecular reorientation. It covers point groups commonly observed in chemical applications, in other words, those which the principal axis of rotation of order equal or lower than 6, and was tested in 18 molecules.