Optimisation par dynamique moléculaire des propriétés structurales des clusters de carbone et de fer, puis étude ab-initio-dft des propriétés électroniques et optoélectroniques des molécules de substances pharmaceutiques.

Abstract

In the first part of this work, we have developed a classical Molecular Dynamics code, in which the interactions between particles of the studied system are described by Gupta's potential. This code has been validated by reproducing the works of Brenner and Kanhere. Then, we used this code to investigate the structural and energetic properties of the ground state of carbon clusters containing from 3 to 120 atoms, as well as iron consisting of 2 to 100 atoms. Our calculations have shown that by using Gupta's potential, the optimized configuration is independent of the choice of the initial configuration. In addition, our results showed a linear behavior of the ground state energy of a cluster as a function of the number N of constituent atoms; and for each type of cluster studied, we established the corresponding analytic relationship; this is an innovative result, which can be useful for predicting the shape, symmetry and properties of an unknown carbon (or iron) cluster. In the second part of this work, using RHF and DFT methods implemented in the Gaussian 03W (2004) code, we investigated the electronic and optoelectric properties of the anthracene, anthraquinone, phenanthrene, quinoline and sulfadoxine molecules and pyrimethamine.We observed that these molecules have high values of hyperpolarizability, electrical susceptibility and refractive index, as well as a low value of the dielectric permittivity. On the other hand, 2- (4-aminophenyl) quinoline, 4- (4-aminophenyl) quinoline, anthracene and anthraquinone are very good organic semiconductors, while phenanthrene is a promising superconductor.At RHF / 6-331 ++ G ** level of theory, we showed that the optoelectrical properties of the pyrimethamine and sulfadoxine molecules are unaffected by solvation. On the other hand, the B3LYP / 6-331 ++ G ** level of theory showed that the dipole moment, the polarizability, the first molecular hyperpolarizability, the polarization density, the average electric field and the displacement vector of sulfadoxine are affected by solvation, while solvation has no effect on the dielectric susceptibility, the dielectric constant, and the refractive index of the same molecule. Geometric optimization and vibrational infra-red intensity analysis of aspirin and ibuprofen molecules were performed using RHF / 6-31 + G * and B3LYP / 6-31 + G * methods.In both cases, our calculations showed that a certain charge transfer took place during the transition from the gaseous phase to the solvated phase.