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Kahn, L. R.

Publications and source records attributed to Kahn, L. R..

7 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Quantum chemical calculation of the equilibrium structures of small metal atom clusters

Metal atom clusters are studied based on the application of ab initio quantum mechanical approaches. Because these large 'molecular' systems pose special practical computational problems in the application of the quantum mechanical methods, there is a special need to find simplifying techniques that do not compromise the reliability of the calculations. Research is therefore directed towards various aspects of the implementation of the effective core potential technique for the removal of the metal atom core electrons from the calculations.

Kahn, L. R.↗
NASA NTRS1981

Quantum chemical calculation of the equilibrium structures of small metal atom clusters

The application of ab initio quantum mechanical approaches in the study of metal atom clusters requires simplifying techniques that do not compromise the reliability of the calculations. Various aspects of the implementation of the effective core potential (ECP) technique for the removal of the metal atom core electrons from the calculation were examined. The ECP molecular integral formulae were modified to bring out the shell characteristics as a first step towards fulfilling the increasing need to speed up the computation of the ECP integrals. Work on the relationships among the derivatives of the molecular integrals that extends some of the techniques pioneered by Komornicki for the calculation of the gradients of the electronic energy was completed and a formulation of the ECP approach that quite naturally unifies the various state-of-the-art "shape- and Hamiltonian-consistent" techniques was discovered.

Kahn, L. R.↗
NASA NTRS1981

Quantum chemical calculation of the equilibrium structures of small metal atom clusters

A decomposition of the molecular energy is presented that is motivated by the atom superposition and electron delocalization physical model of chemical binding. The energy appears in physically transparent form consisting of a classical electrostatic interaction, a zero order two electron exchange interaction, a relaxation energy, and the atomic energies. Detailed formulae are derived in zero and first order of approximation. The formulation extends beyond first order to any chosen level of approximation leading, in principle, to the exact energy. The structure of this energy decomposition lends itself to the fullest utilization of the solutions to the atomic sub problems to simplify the calculation of the molecular energy. If nonlinear relaxation effects remain minor, the molecular energy calculation requires at most the calculation of two center, two electron integrals. This scheme thus affords the prospects of substantially reducing the computational effort required for the calculation of molecular energies.

Kahn, L. R.↗
NASA NTRS1979

Ab initio studies of the electronic structure of UF6, UF6/+/, and UF6/-/ using relativistic effective core potentials

The paper presents ab initio calculations performed on the electronic states of UF6, UF6(+), and UF6(-) using a relativistic effective core potential (ECP) for uranium and a nonrelativistic ECP for fluorine. In most of the calculations 56 valence electrons are treated explicitly using a contracted (3s 3p 2d 2f/2s2p) Gaussian basis. It is noted that various ECP's were explored, but all yield an overall charge density of U(+2.4)/F(-0.4)/6. In addition, the bonding in the ground state of UF6 is discussed. SCF and CI calculations on UF6(+) are compared with the experimental photoelectron spectrum and with previous scattered wave calculations. Further, the role of spin-orbit coupling in the states of UF6(+) and UF6(-) is covered. Finally, it is concluded that the calculated electron affinity of UF6 (7.1 eV) is considerably larger than in current experimental estimates, but the relative energies of the states of UF6(-) are in agreement (0.1-0.2 eV) with those of the experiment.

Hay, P. J.↗