Calcul computationnel des modes vibrationnels d'un dérivé de l'adénine

Abstract

Adéninium hydrate hemisulfate (C5H6N5 +.1/2 SO42- .H2O) is one of the hybrid materials covering a wide range of compounds wherein the structural cohesion is ensured by the hydrogen bonds. Consisting of a nitrogenous base associated with a mineral acid, the computational study spectroscopic vibrational modes allows allocation modes involving hydrogen bonding. Using the Density Functional Theory (DFT) ,calculations of the molecular conformation and frequencies of vibration modes, have been made by the three software; Gaussian, Periodical Gaussian and Vasp.. The hybrid B3LYP functional associated with the base 6-31G (d, p) was used in the Gaussian and functional GGA in the VASP. Calculation results of the isolated molecule, are not in agreement with experimental structural data "cif" the calculated molecular conformation was completely different from that given by experience. Among the calculated frequencies, there were imaginary frequencies. These are the result of an excited state (the molecule is not in its fundamental state). Energy data periodic calculations of molecular conformation given by the VASP agree better with experiment than those obtained by the Gaussian. In the molecular conformation given by the VASP, the adéninium cycle is not planar. This result is at odds with the experience affects the frequencies calculated hence the need to review the data of experience.