David Feller

An approximation to frozen natural orbitals through the use of the Hartree–Fock exchange potential

A modification of a previously defined virtual orbital transformation based on the Hartree–Fock exchange potential is shown to yield a set of orbitals which effectively approximate the frozen natural orbital CI convergence properties.

Ab initio configuration interaction calculations of the hyperfine structure in small radicals

Extended basis set natural orbital CI wave functions have been used to compute the isotropic and anisotropic hyperfine coupling of ten small radicals for which experimental measurements exist. The configuration spaces employed in the CI’s were of two kinds: One involved all single and double excitations from the Hartree–Fock configuration plus limited triples and quadrupoles, while the other consisted of singles and doubles from a multireference set coupled with various configuration selection techniques. At the highest level of theory used in the present study, agreement with experiment was generally within 10%, but differences for the isoelectronic series H2CN, H2CO+, and H2BO as well as the related acetaldehyde radical cation H3C–CHO+ are larger than would be expected based on the data from the other six radicals.

Molecular properties of water

Abstract Extended basis set configuration interaction calculations have been performed on the 1A1 ground state of water at the experimental geometry. Using a wavefunction which yielded the lowest variational energy to date, a variety of molecular properties have been evaluated and their convergence with respect to basis set discussed.

ESR and ab initio theoretical studies of the cation radicals 12C2 16O+2, 12,13C2 16O+2, 13C2 16O+2, 12C2 16,17O+2, 12C2 17O+2, and 12,13C2 16,17O+2 isolated in neon matrices at 4 K. The use of matrix isolation for trapping ion–neutral reaction products

An experimental procedure for generating and trapping the products of ion–neutral reactions has been developed. The method has been applied to a neon matrix ESR study of the C2O+2 radical (X 2Bu) formed during deposition at 4 K by the reaction CO++CO. Six different isotopic combinations of C2O+2 were studied which allowed a complete characterization of the 13C and 17O nuclear hyperfine structure. The experimental A tensors were compared with the results of an extensive SCF and CI theoretical calculation. A full discussion of the theoretical procedure utilized is presented. The electronic ground state was determined by a CI calculation to be the planar trans configuration with a CCO bond angle of 141°. A description of the MO containing the unpaired electron is presented and compared with CO+ and the isoelectronic anion radical C2N−2. The effects of noncoincidence between the g and A tensors are considered in detail for this powder sample of C2O+2 which exhibited relatively narrow ESR lines in a neon matri...

Cardiac Output of Men and Dogs Measured by in vivo Analysis of Iodinated (I131) Human Serum Albumin

A time-intensity analysis of I131 was carried out with a highly shielded well-collimated scintillation detector placed over the chest of normal men and women, patients and dogs. I131 human serum albumin solution was injected intravenously. The curves thus obtained when analyzed for cardiac output gave values not significantly different from simultaneously obtained direct Fick values.

RHF and two-configuration SCF calculations are inappropriate for conjugated diradicals

Abstract Restricted Hartee Fock (RHF) and two-configuration self-consistent field (TCSCF) calculations provide qualitatively correct molecular orbitals for the two open-shell electrons in diradicals. Nevertheless, these calculations fail to give correct relative energies and in some cases they even lead to incorrect geometries. Examples of these failures are given for both singlet and triplet states of some conjugated diradicals. In several cases these failures are related to the “doublet instability problem” in RHF calculations on radicals. It is argued that unrestricted Hartee-Fock (UHF) calculations on triplet states are more likely that RHF to provide accurate geometries.

Relativistic corrections for methylene

Abstract The mass-velocity, Darwin, and magnetic corrections to the 3 P- 5 S and s 2 p 2 -sp 3 splitting of carbon and the 3 B 1 - 1 A 1 splitting in CH 2 have been evaluated by first-order perturbation theory. We obtained corrections of 92 cm −1 for 3 P- 5 S, 100 cm −1 for the s 2 p 2 -sp 3 configuration average and 15 cm −1 for 3 B 1 - 1 A 1 .

The singlet and triplet state rotational potential surfaces for dihydroxycarbene

Potential surfaces have been computed for rotation of the OH groups in C(OH)2 for both the lowest singlet and triplet state. The minima on the singlet surface occur at planar geometries, which represent maxima on the triplet surface. This result is interpreted in terms of different modes of pi electron donation from oxygen being favored in the two states. Evidence is presented that shows pi electron donation is chiefly responsible for making dihydroxycarbene a ground state singlet.

A theoretical determination of the electron affinity of methylene

Large basis set configuration interaction calculations yield an electron affinity of 0.42 eV for CH2(3B1). Application of an empirical correction, based on the known deficiencies of the basis set and CI method in atomic calculations, suggests that this estimate should be increased to approximately 0.63 eV. This provides futher evidence in favor of a reinterpretation of the photoelectron spectrum work of Zittel et al., which indicated an electron affinity of only 0.210 eV while giving a 3B1–1A1 energy gap of 19.6 kcal/mol.

Dependence of the singlet-triplet splitting in heterosubstituted carbenes on the heteroatom electronegativity and conformation

Abstract It is shown by ab initio calculations and by semiquantitative arguments that along the sequence C(NH 2 ) 2 , C(OH) 2 , CF 2 , C(FH) 2 2+ the singlet-triplet gap decreases, due to decreased π bonding, as the substituent electronegativity increases.