Showing papers by "Ernest R. Davidson published in 1973"

Porphyrins XXVIII. Extended Hückel calculations on metal phthalocyanines and tetrazaporphins

Abstract: Extended Huckel (EH) calculations on Mg, Zn, Cu, Ni, Fe, Mn, and VO complexes of phthalocyanine and tetrazaporphin are reported and the results compared to similar calculations on porphyrins The smaller ring size of phthalocyanine gives rise to a larger ligand field The bridge nitrogen atoms give rise to n - π * transitions, which are probably in the region of the Soret band In Ni, Co, Fe, and Mn there is strong mixing of the bridge N2p σ and metal b 2g (d xy ), which should affect the ligand field Extra absorption bands observed in the near uv of NiPc and CoPc are attributed to d π → π * transitions A general symmetrized EH program is reported that speeds calculations on large systems

A configuration interaction study of the spin dipole-dipole parameters for formaldehyde and methylene

Abstract: The electron spin dipole-dipole contribution to the zero field splitting has been evaluated for the 3A2 (n π*) and 3A1 (π π*) states of formaldehyde using a CI wave function constructed from contracted Gaussian-lobe functions. The values D = 0.539 cm−1 and E = 0.031 cm−1 were obtained for the 3A2(n π*) state and D = −0.588 cm−1 and E = 0.058 cm−1 were obtained for the 3A1 (π π*) state using the CI wave function constructed from SCF orbitals of the respective parent configurations. An analysis of the effect of CI on the parameters is given for the 3A2 (nn π*) state of formaldehyde and the 3B1 ground state of methylene. Numerical results are given which show that internally consistent self-consistent field orbitals (ICSCF) are superior to canonical SCF orbitals as a starting point for a CI calculation. Our CI wave function for the 1A1 ground state gave an energy of −114.13658 hartrees which is significantly lower than any previously reported energy calculation. This wave function gives a dipole moment of 2.22 Debye (C+O−) in good agreement with the experimental value of 2.33 ± 0.02 Debye.

An Ab Initio calculation of the spin dipole‐dipole parameters for methylene

Abstract: The electron spin dipole-dipole interaction in CH2 has been calculated as a function of bond angle with configuration-interaction wave functions built from contracted gaussianlobe basis functions The values D = 0781 cm−1 and E = 0050 cm−1 were obtained for the spin dipole-dipole contribution to these parameters for the best CI wave function at the equilibrium geometry The angular dependence of D shows that the assumption of perfect orbital following is not valid Based on previous estimates of the spin-orbit contribution to D, the total D is estimated to be 09 ± 01 cm−1 which is higher than the current experimental value 076 ± 002 cm−1

An ICSCF investigation of Walsh's rules

Abstract: The ICSCF method is applied to the calculation of orbital energies as a function of bond angle for several AH2 molecules. The resulting orbital energy diagrams are quite similar in appearance to the canonical SCF results even though the sum of the ICSCF energies is the SCF energy. The method is also applied to Li2O, CO2, HCN and a few AH3 molecules with similar results. The sum of the ICSCF valence orbital energies generally correlates better with the equilibrium bond angle than does the similar sum of canonical orbital energies.

An Algorithm for the Extreme Rays of a Pointed Convex Polyhedral Cone

Abstract: An algorithm for exhibiting the extreme rays of a pointed convex polyhedral cone is described. The cone is assumed to be initially defined by a system of homogeneous linear inequalities. The method...