Showing papers by "Pacific Northwest National Laboratory published in 1976"

Evaluation of molecular integrals over Gaussian basis functions

Abstract: This paper is concerned with the efficient computation of the ubiquitous electron repulsion integral in molecular quantum mechanics. Differences and similarities in organization of existing Gaussian integral programs are discussed, and a new strategy is developed. An analysis based on the theory of orthogonal polynomials yields a general formula for basis functions of arbitrarily high angular momentum. (ηiηj∥ηkηl) = Σα=1,nIx(uα) Iy(uα) I*z(uα) By computing a large block of integrals concurrently, the same I factors may be used for many different integrals. This method is computationally simple and numerically well behaved. It has been incorporated into a new molecular SCF program HONDO. Preliminary tests indicate that it is competitive with existing methods especially for highly angularly dependent functions.

Relativistic energy levels and bonding in actinide hexaflourides

Abstract: A fully relativistic self‐consistent Dirac–Slater model has been used to calculate one‐electron energy levels and charge distributions for UF6, NpF6, and PuF6. Analysis of ground state charge densities reveals 5fn populations similar to free atom states; we are able to distinguish between metal–ligand bonding levels and the optically active levels described by crystal field theory. Ultraviolet and optical excitations, as well as ionziation energies, are calculated using an approximate transition state procedure and found to be in reasonable agreement with experiment. The Coulomb correlation integral appearing in the determination of the nature of 5f orbitals in solids is discussed on the basis of the systematics observed in our transition state calculations.

Stereochemistry and exchange processes in five-coordinate cobalt(I) complexes containing one of three triphosphine ligands

Abstract: Six extensive series of five-coordinate complexes of the types [Co(triphos)(CO)2]X and [Co(triphos)L(CO)]X (X = BF4, PF6; L = P(OMe)3, PPh2H, PPhzMe, PEt3, PPh3; triphos = either bis(3-dipheny1phosphinopropyl)phenylphosphine (ttp), bis(2-dipheny1phosphinoethyl)phenylphosphine (etp), or l,l,l-tris(diphenylphosphinomethy1)ethane (tripod-P3)) were synthesized and their stereochemistry and dynamic behavior studied principally by 31P(1H] K M R . The details of the stereochemistry and exchange processes depend both on the monodentate ligand and on the triphosphine ligand. For example, the [Co(etp)L(CO)]X and [Co(etp)(C0)2]X complexes are trigonal bipyramidal with the equatorial positions occupied by a carbonyl ligand and the two terminal phosphorus atoms of the triphosphine ligand; the axial positions are occupied by the central phosphorus atom and either a monophosphine or a carbonyl ligand, respectively. The [Co(ttp)L(CO)]X complexes have square-pyramidal structures with L located at the axial position. A trigonal-bipyramidal structure is assigned to the dicarbonyl complexes [Co(ttp)(C0)2]X. The complexes [Co(tripod-P3)L(CO)]X are stereochemically nonrigid, whereas those of [Co(etp)L(CO)]X are stereochemically rigid at room temperature. A large number of 2Jpp coupling constants are presented for these complexes

Biomedical probe using a fiber-optic coupled scintillator.

Abstract: A high-sensitivity biomedical radiation probe which employs a fiber-optic coupled NaI(Tl) scintillator as a detector is described. It was developed for in vivo counting of low-energy 239Pu photons from material located in the tracheobronchial lymph nodes.-This probe is 20 times as sensitive as a solid-state probe (avalanche diode) previously developed for this application. Tests with 99mTc show a sensitivity more than 90 times greater than biomedical probes using DcTe of GaAs; however, the improved sensitivity is largely due to an increased sensitive volume. Probes were evaluated in animals and phantoms for detection of 239Pu and for location of lung tumors labeled with 111In.

14 MeV Neutron damage in molybdenum

Abstract: The radiation damage in molybdenum produced by 14 MeV neutrons has been compared with that produced by fission reactor neutrons. The increased damage level from 14 MeV neutrons compared to fission neutrons as measured by lattice parameter and microstructural changes is much greater than predicted from displaced atom calculations. The damage level measured by electrical resistance changes nearly agrees with the displaced atom calculations. The results are interpreted in terms of an increase in the ratio of clustered defects to free defects after 14 MeV neutron irradiation compared to fission reactor irradiations.

Evaluation of molecular integrals over Gaussian basis functions

Abstract: This paper is concerned with the efficient computation of the ubiquitous electron repulsion integral in molecular quantum mechanics. Differences and similarities in organization of existing Gaussian integral programs are discussed, and a new strategy is developed. An analysis based on the theory of orthogonal polynomials yields a general formula for basis functions of arbitrarily high angular momentum. (ηiηj∥ηkηl) = Σα=1,nIx(uα) Iy(uα) I*z(uα) By computing a large block of integrals concurrently, the same I factors may be used for many different integrals. This method is computationally simple and numerically well behaved. It has been incorporated into a new molecular SCF program HONDO. Preliminary tests indicate that it is competitive with existing methods especially for highly angularly dependent functions.

A Research and Development Decision Model Incorporating Utility Theory and Measurement of Social Values

Abstract: In the research and development environment, the classical decision model, even though modified to include multiple objectives or attributes, fails in the following ways. 1) It uses linear attribute weighting functions. 2) It does not incorporate uncertainty distributions in estimates of total value and attribute attainment. 3) It does not facilitate group decision making. A computer-assisted decision model has been developed to utilize decision analysis information more effectively. A hypothetical analysis of advanced nuclear waste management alternatives illustrates its application. A simulation technique predicts the preferred decision based on estimates of attribute levels, utility functions, and an evaluation of the relative importance of the attributes.