A programmable spin-free method for configuration interaction

In this note a method is presented for quick implementation of configuration interaction (CI) calculations in molecules. A spin-free Hamiltonian for anN electron system in a spin stateS, expressed in terms of the generators for the unitary group algebra, is diagonalized over orbital configurations forming a basis for the irreducible representation [2^1/2N-S 1^2S ] of the permutation group S _N . It has been found that the basic algebraic expressions necessary for the CI calculation involve a limited category of permutations. These have been displayed explicitly. On leave from the Indian Institute of Technology, Bombay, India.     

A study of the oxidation of titanium hydride powder by measurements of its electrical resistance

The oxidation of titanium hydride powder by air oxygen and the influence of oxidation conditions on the degree of oxidation of hydride particles, specific gas content in the powder, and kinetics of its thermal decomposition were studied. The resistometry method was used to determine the effective activation energy of oxidation of titanium hydride by air oxygen. The content of the surface nonconducting phase formed by titanium oxide and oxohydride films under various oxidation conditions was estimated.     

Density functional theory study of NO adsorbed in A-zeolite

Density functional theory was employed to investigate the adsorption site and hyperfine interactions of nitric oxide adsorbed in Na-LTA (previous name NaA) zeolite. Three different cluster models of increasing complexity were used to represent the zeolite network: (1) a six-membered ring terminated by hydrogen atoms with one sodium ion above the ring, (2) as model 1 with the addition of three sodium ions located at the centers of three imagined four-membered rings adjacent to the six-membered ring, and (3) as model 2 with the addition of the three four-membered rings adjacent to the six-membered ring. Calculations on the largest system (model 3) showed very good agreement with measured electronic Zeeman interaction couplings, 14N hyperfine coupling tensors, and 23Na hyperfine and nuclear quadruple coupling tensors of the S = 1/2 Na+...N-O adsorption complex when the position of the sodium ion was relaxed. The optimized geometry of the complex agreed nicely with that estimated experimentally, except for the Na-N distance, where the present results indicate that the distance deduced from previous ENDOR experiments may be underestimated by as much as 0.5 angstroms.     

A uniform estimate for fourier transforms of measures on polynomial curves in ℝ n

We prove a uniform estimate for the decrease of the fourier transforms of smooth measures on polynomial curves in ⁿ . Our estimate improves the estimate recently obtained byW. Stadje.     

Spin-coupled calculations based on projected spin eigenfunctions

It is outlined how the utilization of a basis of projected spin eigenfunctions can lead to increased computational efficiency in the evaluation of matrix elements and density matrices in spin-coupled valence bond calculations. Received: 17 September 1997 / Accepted: 23 October 1997     

Quantum chemical prediction of the adsorption conformations and dynamics at HCOOH‐covered ZnO(1010) surfaces

Results from ab initio Hartree–Fock and gradient‐corrected density functional theory calculations of formic acid interactions with ZnO (101 0) surfaces are reported. Surface relaxation is found to affect equilibrium geometries and adsorption energies significantly. Large variations in adsorption energy with coverage and ordering of the adsorbates are revealed and explained in terms of strong and highly anisotropic electrostatic adsorbate–adsorbate interactions. The results are compared to published experimental and theoretical results, and differences in suggested binding geometries from the different studies are discussed. Dynamic properties of the adsorption, surface mobility, and surface reactivity are inferred from key elements of the potential energy surface obtained from the quantum chemical computations and supported by ab initio molecular dynamics simulations. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

The Hume–Rothery Compound Mn8Ga27.4Zn13.6: Separated Zn13‐Clusters Interspersed in a Primitive Cubic Host Lattice

Separated Zn ₁₃ cluster entities unexpectedly occur in the solid‐state structure of Mn₈Ga_27.4Zn_13.6 (the central building block is shown). They correspond to centered cuboctahedra, that is, small volumes of face‐centered cubic metal. The intriguing segregation of Ga and Zn atoms in Mn₈Ga_27.4Zn_13.6 was verfied by Rietveld refinement of neutron powder diffraction data.     

Representations of the symmetric group generated by projected spin functions: A graphical approach

The representation matrices generated by the projected spin functions have some very interesting properties. All the matrix elements are integers and they are quite sparse. A very efficient algorithm is presented for the calculation of these representation matrices based on a graphical approach and a new indexing scheme for representation of primitive spin functions is introduced. Test calculations show that the method is very fast and suited for calculations on vector computers. © 1996 John Wiley & Sons, Inc.