Mingzuo Shen

The dodecahedral N20 molecule. Some theoretical predictions

Abstract Ab initio quantum mechanical methods have been applied to the Ih point group isomer of N20. Dodecahedral N20 is predicted to be a relative minimum on its potential energy hypersurface, lying above separated nitrogen molecules by about 50 kcal per mol of nitrogen atoms. Vibrational frequencies, infrared intensities, and ionization potentials are also predicted.

Hydrogen bonding between the nitrate anion (conventional and peroxy forms) and the water molecule

Ab initio quantum mechanical methods have been applied to the complexes of the nitrate anion (conventional D3h NO−3 and Cs ONOO− forms) with the water molecule, namely, NO−3⋅H2O and ONOO−⋅H2O. Equilibrium geometries and vibrational frequencies for a number of energy minima on the ground state potential energy surface have been determined using analytic energy first and second derivative techniques. The highest level of theory employed is the self‐consistent field method with a double‐zeta plus polarization basis set. The minimum energy structure (lying ∼15 kcal/mol below separated NO−3 +H2O) incorporates two hydrogen bonds in C2v symmetry. This theoretical dissociation energy agrees well with experiment. A second, more conventional single‐hydrogen‐bond structure is predicted to lie 2.6 kcal/mol higher in energy. At the most reliable level of theory, no distinct minimum was found for the hydrogen bonded structure between HNO3 (nitric acid) and OH−. Several minima (high lying energetically) between ONOO− an...

The known and unknown group 13 hydride molecules M2H6: Diborane(6), dialane(6), and digallane(6)

Molecular structures, harmonic vibrational frequencies, and infrared intensities for diborane B2H6, dialane Al2H6, and digallane Ga2H6 have been determined using high level ab initio quantum mechanical methods. The highest level of theory employed in this study is the single and double excitation coupled cluster (CCSD) method with double‐zeta plus polarization (DZP) basis sets. This study serves to assess the reliabilities of various theoretical methods, laying the foundation for future theoretical studies of larger boron, aluminum, and gallium molecular systems. It appears that the theoretical methods employed here are adequately reliable when compared with existing experiments. Several shortcomings of previous ab initio quantum mechanical studies on diborane(6) and its analogs have been addressed.

Dodecahedral and smaller arsenic clusters: Asn, n=2, 4, 12, 20

Ab initio all‐electron quantum mechanical methods, including the Hartree–Fock (HF), second‐order perturbation theory, configuration interaction with single and double excitations (CISD), and coupled cluster with single and double excitations (CCSD) methods, have been applied to four arsenic clusters, diatomic As2, tetrahedral As4, cagelike As12 belonging to the D3d point group, and dodecahedral As20. Several basis sets were used. The double‐zeta plus polarization (DZP) includes both d and f polarization functions, while the triple‐zeta plus double polarization basis includes two sets of f functions on each atom. From the most reliable theoretical results, As12 is energetically lowest among the clusters considered, and As20 is energetically comparable to As4.

Tungsten hexahydride (WH6). An equilibrium geometry far from octahedral

Ab initio all‐electron quantum mechanical methods were applied to the tungsten hexahydride (WH6) molecule using very large basis sets. Seven distinct structures were investigated with full geometry optimizations at the self‐consistent field (SCF) level of theory. The effects of electron correlation were estimated with second‐order Mo/ller–Plesset perturbation theory (MP2), modified coupled pair functional (MCPF) method, and the coupled cluster with single and double excitations (CCSD) method, and relativistic effects estimated using the Cowan–Griffin (mass–velocity and Darwin) corrections. Our results suggest that the ground state of the tungsten hexahydride (WH6) molecule is a closed‐shell triangular prism belonging to the C3v point group, with a set of three hydrogens stacked on top of another set of three hydrogens. From the perspective of inorganic chemistry, it is truly remarkable that the octahedral structure lies 130 kcal/mol above the C3v ground state. Furthermore, these results imply major qualit...

Toward the infrared spectroscopic observation of SiH+5: the silanium ion

Ab initio quantum mechanical methods, including the self-consistent field, single and double excitation configuration interaction, and single and double excitation coupled cluster, have been applied to six stationary points on the SiH+5 potential energy hypersurface. Equilibrium geometries were determined using analytic energy first derivative techniques. Relative energies of stationary points have been obtained. Harmonic vibrational frequencies of the global minimum were obtained at all levels of theory. Basis sets used include double-zeta plus polarization and triple-zeta plus double polarization. SiH+5 should be regarded as involving weakly bound H2 and SiH+3 subunits, with a dissociation energy of only about 10 kcal/mol. Pseudorotation was found to be unfavorable in the SiH+5 ion.

Is dodecahedral P20 special

SummaryThe laboratory study of phosphorus clusters by laser-based mass spectrometric methods indicates, tentatively, that P+21 may be special. A plausible interpretation might place a P+ ion interior to a dodecahedral P20 molecule.Ab initio quantum mechanical methods have been applied to the P20 molecule using contracted gaussian basis sets as large as (9s 6p 4d 3f) on each phosphorus atom. At the highest level of theory, dodecahedral P20 is predicted to lie 23 kcal/mol above five separated P4 molecules.

The tetramer of borane and its heavier valence-isoelectronic analogs: M4H12 with M = B, Al, and Ga

Abstract Ab initio all-electron quantum mechanical methods were applied to the tetramers of borane (BH 3 ) and its analogs in the periodic table, namely the molecules B 4 H 12 (tetraborane (12) or (BH 3 ) 4 ), Al 4 H 12 (tetraalane (12) or (AlH 3 ) 4 ), Ga 4 H 12 (tetragallane (12) or (GaH 3 ) 4 ). Four closed-shell stationary points were found for each tetramer. In addition, the butterfly tetraborane (10) (B 4 H 10 ) and its analogs tetraalane (10) (Al 4 H 10 ) and tetragallane (10) (Ga 4 H 10 ) were investigated at comparable levels of theory. Geometry optimizations were performed at correlated whenever practical, and at the Hartree-Fock level otherwise, using sizeable basis sets. In most cases, energetic information was obtained from correlated methods. It is confirmed that the most recent (1981) experimental structures for tetraborane (10) have an error for one of the bridging BH bond distances, as noted recently by Buhl and Schleyer. However, the other three experimental structures for B 4 H 10 also have serious problems. Our results suggest that the molecular structures of butterfly M 4 H 10 , M = B, Al, Ga, are very similar. The structures of M 4 H 12 , M = B, Al, Ga, although still quite similar, show more variations. We found that the butterfly (12) structures, belonging to the point group C 2v , are local minima at the SCF potential energy surfaces. The butterfly tetraborane (12) is energetically less stable than the butterfly tetraborane (10) plus molecular hydrogen. The butterfly tetraalane (12) is, in contrast, energetically more stable than the butterfly tetraalane (10) plus molecular hydrogen. The butterfly tetragallane (12) displays a third behavior - energetically comparably stable with the butterfly tetragallane (10) plus molecular hydrogen. In all cases electron correlation effects were found to stabilize the butterfly (10) structures more than the butterfly (12) structures.

The H2O2-NO2− and H2NO4− isomers of the nitrate anion-water complex

Abstract Ab initio quantum mechanical methods have been applied to two isomers of the complex of the conventional nitrate anion (D 3h NO 3 − ) with the water molecule, namely, H 2 NO 4 − (two conformers) and H 2 O 2 -NO 2 − . The nitrogen atom in H 2 NO 4 − is tetrahedrally coordinated to the four oxygen atoms, while H 2 O 2 -NO 2 − is a doubly hydrogen-bonded system. Equilibrium geometries and vibrational frequencies for these three energy minima on the ground state (singlet) potential energy surface have been determined using analytic energy first and second derivative techniques. The standard level of theory employed is the self-consistent-field (SCF) method with a double-zeta plus polarization (DZP) basis set. However, the effects of diffuse basis set and electron correlation effects were also carefully considered. At this level of theory, all three structures studied lie energetically well above the complex between the conventional nitrate anion and the water molecule. The system H 2 O 2 -NO 2 - , with two strong, equivalent, and nearly linear hydrogen bonds, lies energetically closest (∼46 kcal/mol) to the nitrate anion-water molecule complex.

The silyl anion (SiH−3): Cubic/quartic force field and anharmonic contributions to the fundamental vibrational frequencies

Fundamental vibrational frequencies for the silyl anion have been determined using two distinct vibrational theoretical methods, namely, the standard second‐order perturbation theory and Pulay’s variational theory. Several full quartic force fields were determined and used in both vibrational methods. Ab initio quantum mechanical methods used to generate energy derivatives include self‐consistent‐field (SCF), configuration interaction with single and double excitations (CISD), and coupled cluster with single and double excitations (CCSD), in conjunction with basis sets including double zeta plus polarization (DZP), triple zeta plus double polarization (TZ2P), and TZ2P plus diffuse p functions on the silicon atom [TZ2P+diff(Si)]. SCF energy third derivatives were determined using analytic methods, while SCF fourth derivatives were determined from finite differences of third derivatives. CISD analytic energy gradients were used to generate second, third, and fourth derivatives by finite difference methods. ...