Acetylene, Vinylidene, and the Vinyl Cation in Ground and Excited States

Ab initio calculations using the improved virtual orbital formalism are reported for acetylene, vinylidene, and the vinyl cation, C2H,+, in classical and bridged geometries. Electronic transition energies and equilibrium geometries for ground and lower lying electronically excited states have been calculated. A modified Walsh diagram for acetylene and simple molecular orbital considerations explain excited state structures and energy orderings. While acetylene in the ground state is much more stable than vinylidene, the energies of several corresponding excited states are comparable. The stabilities of bridged and classical structures of the vinyl cation are very similar in the ground state, but in the various excited states either strcture can predominate. The proton affinity of acetylene in the ground state should be appreciably lower than in excited states

Ab initio prediction of Boron compounds arising from Borozene: Structural and electronic properties

Structure and electronic properties of two unusual boron clusters obtained by fusion of borozene rings has been studied by means of first principles calculations, based on the generalized-gradient approximation of the density functional theory, and the semiempirical tight-binding method was used for the transport calculations. The role of disorder has also been considered with single vacancies and substitutional atoms. Results show that the pure boron clusters are topologically planar and characterized by (3c-2e) bonds, which can explain, together with the aromaticity (estimated by means of NICS), the remarkable cohesive energy values obtained. Such feature makes these systems competitive with the most stable boron clusters to date. On the contrary, the introduction of impurities compromises stability and planarity in both cases. The energy gap values indicate that these clusters possess a semiconducting character, while when the larger system is considered, zero-values of the density of states are found exclusively within the HOMO-LUMO gap. Electron transport calculations within the Landauer formalism confirm these indications, showing semiconductor-like low bias differential conductance for these stuctures. Differences and similarities with Carbon clusters are highlighted in the discussion.Comment: 10 pages, 2 tables, 5 figure

The Structural Variations of Monomeric Alkaline Earth MX2_2-Compounds (M = Ca, Sr, Ba; X = Li, BeH, BH2_2, CH3_3, NH2_2,OH, F). An ab Initio Pseudopotential Study

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Do Low-Coordinated Group 1-3 cations Mn^n +^+Lm_m (Mn+^+ = K+^+, Rb+^+, Cs+^+, Ca2+^{2+}, Sr2+^{2+}, Ba2+^{2+}, Sc3+^{3+}, Y3+^{3+}, La3+^{3+}; L = NH3_3, H2_20, HF; m = 1-3) with a Formal Noble-Gas Electron Configuration Favor Regular or "Abnormal" Shapes?

No abstract availabl

The Structure and Stability Trends Fluoro(methyl)plumbanes

No abstract availabl