Interpretation of Open-Shell SCF Calculations on the T and V States of Ethylene

Self-consistent field calculations are reported on (planar and perpendicular geometric conformers of) the lowest energy triplet and singlet (pi,pi*) orbital configurations of ethylene, which are usually identified with the spectroscopic T and V states, respectively. For the planar conformation the calculation predicts a V state with the characteristics of a Rydberg state, but a T state of expected valence-shell character. The pi* orbital is much too large and the internuclear distance too small for the calculated V state, but are as expected for the T state. It is concluded that the calculated result for the supposed V state in the planar conformation is spurious due to the inadequacy of the Hartree–Fock single-configuration theory. The supposed V state here calculated may be identified with a Rydberg state which has been observed spectroscopically at ~ 1.4 eV higher energy than the V state in the optical spectrum. For the perpendicular conformation, the calculations yield resonable results for both the T and V states. Calculations also have been carried out on a singlet (sigma,pi*) state for planar ethylene; here the size of the pi* orbital is reasonable

Molecular Orbital Theory for Octahedral and Tetrahedral Metal Complexes

Self-consistent charge and configuration (SCCC) molecular orbital calculations are reported for 32 selected octahedral and tetrahedral first-row transition-metal complexes containing halide and chalcogenide ligands. It is found that for the range of metal oxidation states II through IV, Fsigma, chosen to fit the experimental Delta, is a function of only the metal atomic number for constant Fpi. In the range of formal metal oxidation numbers V through VII, Fsigma is also a function of oxidation number.Calculated and observed trends in covalency, Delta values, and first L-->M charge-transfer energies are compared. The conclusion is drawn that the molecular orbital method, in its present formulation, gives a reasonable account of the ground states and low excited states in simple metal complexes

An Effective Fragment Method for Modeling Solvent Effects in Quantum Mechanical Calculations

An effective fragment model is developed to treat solvent effects on chemical properties andreactions. The solvent, which might consist of discrete water molecules, protein, or othermaterial, is treated explicitly using a model potential that incorporates electrostatics,polarization, and exchange repulsion effects. The solute, which one can most generally envision as including some number of solvent molecules as well, is treated in a fully ab initio manner, using an appropriate level of electronic structure theory. In addition to the fragment model itself, formulae are presented that permit the determination of analytic energy gradients and, therefore, numerically determined energy second derivatives (hessians) for the complete system. Initial tests of the model for the water dimer and water‐formamide are in good agreement with fully abinitio calculations

OPTICAL SPECTRA AND PROPERTIES OF SMALL RINGS

Author Institution: Scientific Laboratory; Bell Telephone LaboratoriesThe electronic structure and properties of cyclopropene, diazirine, cyclopropane, ethylene oxide, ethyleneimine, and diaziridine have been obtained from large gaussian orbital basis SCF-MO computed molecular wave functions. These are used to interpret newly obtained optical spectra in the vacuum ultraviolet region and photoelectron ionization potential data for these molecules