الفهرس | Only 14 pages are availabe for public view |
Abstract The thesis comprises three chapters and two appendices. The first chapter includes an introduction, a literature survey and the aim of this work. Historical background about the density functional theory (DFT) was given. The different theories were presented and the accuracy of calculations for each theory was shown. The accuracy of predicted atomization energies was within 3-5 kcalJmol, and bond lengths and bond angles were within a few percent of corresponding experimental values. However, G2, BlL YP, and even the recently Bx88IBc95 methodologies scaled as ~ :N7, ~, and N5, respectively, where N is the number of the basis functions. Therefore, there was a need for a novel method that scales as N3 to apply to large chemical systems. In the second chapter, it was my objective to derive the basic working equations in OFT. The starting point was the definition of the Schrodinger equation. The concepts of Density functional theory were shown, together with a comparison of these equations with corresponding ones obtained from Hartree-Fock theory. The solution of the DFT equations was given. Molecular orbital theory and basis sets were described. The development of the new DFT model (HFS-BVWN) that will be used throughout this work was presented. The third chapter of the thesis deals with the results and discussion. The calculated atomic and molecular energies using HFS-BVWN/6- 311+g(3df,p) method are on the average 0.13% higher than the corresponding correlated HF values. The reported method is thus expected to underestimate molecular exchange-correlation energIes by more than 0.13%. Application of atom equivalent scheme (AES) in connection with the results of HFS-BVWN/6-311 +g(3df,p) computations gave the corrected atomic energies for hydrogen through chlorine (H-C!). The room temperature heats of formation for 118 molecules and radicals are calculated from the results of HFS-BVWN/6-311 +g(3df,p) computations and the derived atom equivalents. The average absolute error in calculated enthalpies of formation is 1.8 kcaUmol. The corresponding average errors in G2, Bx88/Bc95, B3LYP and BLYP theories are 1.2, 2.0, 2.4 and 3.94 kcallmol respectively. Also the ionization potentials and the electron affinities of the ions of the atoms of the first two rows of the periodic table and some selected molecules and radicals are calculated from the results of HFS-BVWN/6-311+g(3df,p) method. For ionization potentials (IPs) the average absolute deviation is 0.12 eV, compared with 0.195 eV for BLYP, 0.l4 eV for B3LYP, 0.12 eV for Bx88/Bc95 and 0.05 eV for G2. The calculated electron affinities have an average deviation of 0.13 eV, excluuing hydrogen, compared with 0.08 eV for G2 and 0.14 eV forBLYP. |