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Structure and bonding in Al3O n and Al3O n - aluminum oxide clusters where n = 1−3 are studied with electronic structure calculations and are compared with some experimental results. Geometry optimizations with the B3LYP/6-311+G(2d,p) density functional method produced minima which were verified with frequency calculations. Several initial geometries and distinct spin multiplicities were considered for each case. The most stable anionic structures from density functional calculations were confirmed with additional geometry optimizations at the QCISD level. Equilibrium geometries, harmonic frequencies, and atomic charges are presented. These results, in combination with previous assignments of anion photoelectron spectra, provide a consistent explanation for changes in isomerization energies between anionic and neutral species.

The electronic structure of small (∼1 nm) silicon nanocrystals passivated with nitrogen and chlorine is explored using density funcional theory calculations. The HOMO-LUMO gap of 3.2 and 3.3 eV, calculated for the fully nitrogen [Si 35 (NH 2 ) 36 ] and chlorine passivated (Si 35 Cl 36 ) nanocrystals, respectively, correlate quite well with experimental observations describing the blue and/or white photoluminescence and electroluminescence of silicon nanocrystals, embedded in chlorinated silicon nitride films. On the other hand, the ionization energy and the electron affinity allow us to study the electron transfer properties of these systems. The chargetransfer capacity of these nanocrystals is modified in opposite directions with respect to hydrogen-passivated nanocrystals, becoming good electron acceptors with Cl passivation and good electron donors with NH 2 passivation.

Density functional theory calculations and theoretical representations of the density of states (DOS) were undertaken in order to understand the electronic properties of silicon nanocrystals (Si-nc), when partially passivated with Cl and F. Effects relating to cluster size (Si29, Si35, and Si87), type, and percentages of halogen surface passivant, concerning both the cluster gap and electron-donor–acceptor capabilities, were analyzed. These calculations indicate that as the percentage of Cl and F substitution increases, the energy of the LUMO decreases, and consequently, the HOMO–LUMO gap decreases. Correspondingly, we found that the high-electronegativity substituent Cl and F atoms produce the appearance of shoulders in the DOS band edges, thus reducing the band gap. These results explain the photoluminescent experimental data reported for Si-nc. The evaluation of the electrodonating and electroaccepting powers of Si-nc partially passivated with Cl and F indicates that Si-nc have potential applications for bulk heterojunction solar cells and electroluminescent devices.

A systematic study of the structural properties and electronic structure of six phases of C 3 N 4 is presented. The phases under study are the β, α, cubic, pseudocubic and two graphitic with different space group. The structural analysis shows that only in β and graphitic phases the N atoms behave in a pure sp 2 configuration. In the other phases, α, cubic and pseudocubic, the N with its 3 C neighbors form a pyramid. The band structure for each of the six phases is presented indicating with β, α and cubic phases have an indirect gap while the pseudocubic and the two graphitic phases have a direct gap. Also charge density contours are presented and analyzed.