Microcanonical thermodynamics and statistical fragmentation of dissipative systems. The topological structure of the N-body phase space

The family of correlation consistent polarized valence basis sets has been extended in order to account for core−core and core−valence correlation effects within the third-row, main group atoms gallium through krypton. Construction of the basis sets is similar to that of the atoms boron through argon, where either the difference between core-correlated and valence-only correlation energies were calculated via configuration interaction (CISD) computations on the ground electronic states of the atoms (named cc-pCVnZ) or the sets were optimized with respect to the core−valence correlation energy and a small weight of core−core correlation energy (cc-pwCVnZ). Due to the correlation of 3d orbitals, added shells of higher angular momentum exponents compared to the valence sets are necessary to describe the core region. The pattern of added core-correlating functions is (1s1p1d1f) for double-ζ, (2s2p2d2f1g) for triple-ζ, (3s3p3d3f2g1h) for quadruple-ζ, and (4s4p4d4f3g2h1i) for quintuple-ζ. Atomic and molecular r...

Systematically convergent correlation consistent basis sets for molecular core-valence correlation effects: the third-row atoms gallium through krypton.

Previous calculations of the structures of isomers of phosphorus clusters up to P11 (density functional calculations with simulated annealing, local spin density approximation to the exchange‐correlation energy) have been extended to arsenic clusters. The structures of Asn clusters are characterized by an almost uniform expansion (∼ 9%) of the corresponding Pn isomers. All cluster isomers have also been studied using a nonlocal, gradient corrected (Becke–Perdew) energy functional. While the structures are almost unchanged, there are significant improvements in the cohesive energies of all clusters. We present a simple picture to show that the improvements arise from contributions both in the atoms and near the ‘‘surface’’ of the clusters.

Density functional study of phosphorus and arsenic clusters using local and nonlocal energy functionals

The electronic structure and chemical bonding of the pentapnictogen cluster anions, Pn5- (Pn = P, As, Sb, and Bi), were investigated using both photoelectron spectroscopy and ab initio calculations. Well-resolved photoelectron spectra were obtained for the anions at several photon energies and were analyzed according to the theoretical calculations. The ground state of all the Pn5- species was found to be the aromatic cyclic D5h structure with a C2v low-lying isomer. We found that the C2v isomer gains stability from P5- to Sb5-, consistent with the experimental observation of the coexistence of both isomers in the spectra of Sb5-. The valence molecular orbitals (MOs) of the D5h Pn5- were analyzed and compared to those of the aromatic C5H5- hydrocarbon. The same set of π-MOs is shown to be occupied in the D5h Pn5- and C5H5- species, except that the MO ordering is slightly different. Whereas the three π-MOs in C5H5- all lie above the σ-MOs, the third π orbital (1a2‘ ‘ in Pn5-) lies below the σ-MOs. The stab...

Probing the Electronic Structure and Aromaticity of Pentapnictogen Cluster Anions Pn5- (Pn = P, As, Sb, and Bi) Using Photoelectron Spectroscopy and ab Initio Calculations

Geometries and energy separations of ten electronic states of Ge4, Sn4, and Pb4 are computed and compared with Si4. We employ complete active space multiconfiguration self‐consistent‐field followed by multireference singles + doubles configuration interaction calculations. The ground states of Ge4–Pb4 are found to be 1Ag states with equilibrium geometries of rhombus similar to Si4. Relativistic effects are found to be significant for Pb4. Atomization/dissociation energies of Ge4–Pb4 are computed and compared with Si4. Pb4 was found to be considerably less bound compared to other tetramers. The energy separations of the excited electronic states were found to decrease, especially the splitting between the rhombus and tetrahedral structures, as one goes down the group.

Electronic structure of group IV tetramers (Si4–Pb4)

The HeI (584 A) high resolution photoelectron spectra of As+2, Sb+2, and Bi+2 have been obtained with a high temperature molecular beam source. A pure As2 beam was produced by evaporating Cu3As. Sb2 was generated as a mixture with the atoms and tetramers by evaporating the pure element, while Bi2 was generated as a mixture with only the atoms from the pure element. Vibrational structure was well resolved for the As+2 spectrum. Spectroscopic constants were derived and reported for the related ionic states. In addition, we have carried out relativistic complete active space self‐consistent field followed by multireference single + double configuration interaction calculations on these dimers both for the neutral ground states and the related ionic states. The agreements between the calculated and experimentally derived spectroscopic constants were fairly good, although the calculations tended to underestimate consistently the strength of the bonding in these heavy homonuclear diatomics.

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P. Feng

Papers

Photoelectron spectroscopy and electronic structure of clusters of the group V elements. I, Dimers