Benchmarking and application of density functional methods in computational chemistry
Papas, Brian Nicholas
MetadataShow full item record
Density Functional methods were applied to systems of chemical interest. First, the effects of integration grid quadrature choice upon energy precision were documented. This was done through application of DFT theory as implemented in five standard computational chemistry programs to a subset of the G2/97 test set of molecules. Subsequently, the neutral hydrogen-loss radicals of naphthalene, anthracene, tetracene, and pentacene and their anions where characterized using five standard DFT treatments. The global and local electron affinities were computed for the twelve radicals. The results for the 1- naphthalenyl and 2-naphthalenyl radicals were compared to experiment, and it was found that B3LYP appears to be the most reliable functional for this type of system. For the larger systems the predicted site specific adiabatic electron affinities of the radicals are 1.51 eV (1-anthracenyl), 1.46 eV (2-anthracenyl), 1.68 eV (9-anthracenyl); 1.61 eV (1-tetracenyl), 1.56 eV (2-tetracenyl), 1.82 eV (12-tetracenyl); 1.93 eV (14-pentacenyl), 2.01 eV (13-pentacenyl), 1.68 eV (1-pentacenyl), and 1.63 eV (2-pentacenyl). The global minimum for each radical does not have the same hydrogen removed as the global minimum for the analogous anion. With this in mind, the global (or most preferred site) adiabatic electron affinities are 1.37 eV (naphthalenyl), 1.64 eV (anthracenyl), 1.81 eV (tetracenyl), and 1.97 eV (pentacenyl). In later work, ten (scandium through zinc) homonuclear transition metal trimers were studied using one DFT functional. Electronic ground states and bond lengths for equilateral triangles were: Sc3 (2A1 ' , 2.83 Å), Ti3 (7E ' , 2.32), V3 (2E . , 2.06), Cr3 (17E ' , 2.92), Mn3 (16A2 ' , 2.73), Fe3 (11E . , 2.24), Co3 (6E . , 2.18), Ni3 (3A2. , 2.23), Cu3 (2E ' , 2.37), Zn3 (1A1 ' , 2.93). Vibrational frequencies, several low-lying electronic states, and trends in bond lengths and atomization energies are discussed. The predicted dissociation energies .E (M3 . M2 + M) are 49.4 kcal mol-1 (Sc3), 64.3 kcal mol-1 (Ti3), 60.7 kcal mol-1 (V3), 11.5 kcal mol-1 (Cr3), 32.4 kcal mol-1 (Mn3), 61.5 kcal mol-1 (Fe3), 78.0 kcal mol-1 (Co3), 86.1 kcal mol-1 (Ni3), 26.8 kcal mol-1 (Cu3), and 4.5 kcal mol-1 (Zn3).