Showing papers by "Ernest R. Davidson published in 1989"

Energy partitioning of the self‐consistent field interaction energy of ScCO

Abstract: The SCF interaction energy for ScCO was partitioned into the electrostatic, polarization, exchange, and charge‐transfer terms via the Morokuma analysis This definition of polarization does not satisfy the Pauli exclusion principle and therefore, there is nothing to prevent the valence electrons of one fragment from collapsing into the core orbitals of the other fragment To correct this problem, the polarization and charge‐transfer terms were calculated in the presence of exchange The dominant interactions were exchange repulsion, electrostatic attraction, and distortion of the wave function by polarization and charge transfer Pi backbonding was the dominant distortion for the 4 Σ− 4s1 3dπ2 state, while sigma distortions dominated the 4s2 3d 1 states

Electron spin resonance investigations of 11B12C, 11B13C, and 10B12C in neon, argon, and krypton matrices at 4 K: Comparison with theoretical results

Abstract: The first spectroscopic study of the diatomic radical BC is reported which confirms previous theoretical predictions of a 4∑− electronic ground state. The nuclear hyperfine interactions (A tensors) obtained for 11B, 10B, and 13C from the electron spin resonance (ESR) measurements are compared with extensive ab initio CI calculations. The BC molecule is one of the first examples of a small high spin radical for such an in‐depth experimental–theoretical comparison. The electronic structure of BC obtained from an analysis of the nuclear hyperfine interaction (hfi) is compared to that obtained from a Mulliken‐type population analysis conducted on a CI wave function which yields Aiso and Adip results in good agreement with the observed values. The BC radical was generated by the laser vaporization of a boron–carbon mixture and trapped in neon, argon, and krypton matrices at 4 K for a complete ESR characterization. The magnetic parameters (MHz) obtained for 11B13C in solid neon are: g∥ =2.0015(3); g⊥ =2.0020(3); D(zfs)=1701(2); 11B: ‖A∥‖ =100(1); ‖A⊥‖ =79(1); 13C: ‖A∥‖ =5(2) and ‖A⊥‖ =15(1). Based on comparison with the theoretical results, the most likely choice of signs is that all A values are positive.

The electron affinity of oxygen: A systematic configuration interaction approach

Abstract: A sequence of configuration interaction (CI) wave functions, constructed so as to systematically approach the complete basis set, full CI limit, is used to argue that the only alternatives for improving the accuracy of electron affinity calculations are: (1) recovery of a sufficient fraction of the correlation energy of both anion and neutral so that the remaining error in the energy difference is acceptably small, or (2) methodological bias in favor of the more difficult to describe anion. Extended Gaussian basis sets, of the type recently employed in atomic hyperfine spin calculations are capable of recovering 95%–96% of the total O (3P) correlation energy. With much greater difficulty this basis can also recover an equivalent fraction of the O− (2 P) correlation energy. Nevertheless, the calculated electron affinity(1.31 eV) still underestimates the experimental value of 1.46 eV by 10%. Estimates based on multireference second order pertubation theory suggest that another 0.05 eV (EA=1.36 eV) is availa...

A Theoretical Study of Models for X2Y2 Zintl Ions

Abstract: Ab initio and extended Hueckel calculations have been used to discuss the bonding scheme in X{sub 2}Y{sub 2} neutral and ionic main group clusters. A qualitative analysis suggests that two different electron counts, 20 and 22, are possible for the butterfly structures of these systems. This results from two orbital crossings in the correlation diagram for the tetrahedral (T{sub d}) {yields} butterfly (C{sub 2{nu}}) {yields} square-planar (D{sub 2h}) transformation. Detailed ab initio computations substantiate this analysis and show that the 20-electron butterfly structure becomes increasingly favored over the tetrahedral one in X{sub 2}Y{sub 2} clusters when the 2 atoms have increasing electronegativity difference. These results are in agreement with the known structures for the Pb{sub 2}Sb{sub 2}{sup 2{minus}} and Sb{sub 2}Bi{sub 2}{sup 2{minus}} clusters (tetrahedral-like) and the Tl{sub 2}Te{sub 2}{sup 2{minus}} one (butterfly-like).

Analysis of the bond energy of ScCO

Abstract: In this paper, the self‐consistent‐field (SCF) and correlated bond energies in ScCO were examined. At the SCF level, the bond energy was determined to consist primarily of the s→d promotion energy of the metal, the CO distortion energy, and the SCF interaction energy which is the combined effect of the σ and π interactions. Corrections to the SCF bond energy to obtain the correlated bond energy of the complex were determined to be mainly the dispersion energy of the complex, the correlation corrections to the SCF CO distortion energy, and the correlation and relativistic corrections to the SCF scandium promotion energy.

AM1 studies on the potential energy surface for the proton transfer in protonated water clusters, H+(H2O)n

Abstract: The potential energy surfaces for the proton transfer processes in H+(H2O)n with n=2 ∼ 11 have been studied using the semiempirical AM1 method. Two model systems were adopted: branched and linear systems. The branched system showed a tendency to form a bulk cluster, while the linear system showed a tendency toward a constant barrier height with increasing number of water molecules in the model system. The potential energy surfaces were discussed using Marcus theory. In the case of H+ (H2O)n with n=10 and 11, the intrinsic barrier to the proton transfer was found to be around 1.0 kcal/mol.