Sobre els mapes de semblança quàntica molecular

Abstract

Partint de les definicions usuals de Mesures de Semblança Quàntica (MSQ), es considera la dependència d'aquestes mesures respecte de la superposició molecular. Pel cas particular en qnè els sistemes comparats siguin una molècula i un Àtom i que les mesures es calculin amb l'aproximació EASA, les MSQ esdevenen funcions de les tres coordenades de l'espai. Mantenint fixa una de les tres coordenades, es pot representar fàcilment la variació del valor de semblança en un pla determinat, i obtenir els anomenats mapes de semblança. En aquest article, es comparen els mapes de semblança obtinguts amb diferents MSQ per a sistemes senzills

Quantum Similarity Measures (QSM) allow to compare quantitatively any pair of molecules or, in general, quantum systems. Severa1 definitions of QSM exist, but, in all cases, these measures are dependent on the mutual superposition of the molecules or systems compared. In this paper, QSM between a molecule and a single atom are considered. Within the EASA approximation, which considers atoms as having spherical simmetry, these measures depend only on three spatial coordinates, and can be thus considered as spatial functions. By fixing one of these coordinates, the so called QSM maps can be easily obtained, representing the variation of the QSM value throughout a region of a plane. Some of these maps were obtained for the benzene 1 nitrogen and chlorobenzene / nitrogen systems, using different QSM and computational schemes. In all cases, the topology of the QSM maps matches a pattern defined by the heavy atoms of the considered molecule, while hydrogen atoms are nearly ignored in the map. This follows the well-known fact that maximal density values in molecules are located over the atomic coordinates, and suggests a close connection between QSM maps and the molecular density function. Comparisons of QSM maps of the same system helps to show the behaviour of different operator QSM. QSM maps have also been useful in order to test some of the computational schemes used in the EASA QSM computation