Ch. Chang

Electronic structure investigation of neutral titanium oxide molecules TixOy

Electronic and structural properties of energetically low-lying isomers of isolated TixOy (x = 1-6, y = 1-12) molecular systems have been investigated by density functional theoretical methods. A variety of stationary points are thoroughly characterized. We report total cluster energies, equilibrium geometries and harmonic vibrational wavenumbers.

A density functional study of small (AlN)x clusters: structures, energies, and frequencies

Abstract Structural properties of energetically low-lying stationary points of small aluminium/nitrogen clusters with unity stoichiometric ratio (AlN)x (x=1,2,4,6,12) have been investigated by theoretical density functional techniques employing the Becke–Perdew-86 gradient corrected exchange correlation functional. A large number of singlet and triplet stationary points representing local minima and transition structures of (AlN)x are completely characterised. We report energies, equilibrium geometric parameters, selected harmonic vibrational wave numbers along with corresponding absorption coefficients. Stability and geometric aspects of (AlN)12 are discussed in detail by introducing a measure of sphericity.

Electronic structure investigation of the Al4O4 molecule

Abstract Structural properties of energetically low-lying isomers of the isolated Al 4 O 4 molecular system have been investigated by theoretical ab initio techniques within the Hartree–Fock (HF) and second-order Moller–Plesset (MP2) frozen core level of approximation and density functional methods (DFT) employing the Becke-3–Perdew-86 (B3P86) hybrid functional. In total, nine local minima representing six Al 4 O 4 isomers of various spin multiplicities are completely characterised. The two energetically lowest of these stationary points, a singlet of planar D 2 h and a triplet of cubic T d symmetry, are furthermore sifted by considering other choices of exchange (B, B3) and correlation (LYP, PW91) functionals as well as higher levels of theory (G2/MP2, G2, and CCSD(T), D 2 h only). We report energies, equilibrium geometric parameters, selected harmonic vibrational wavenumbers along with corresponding absorption coefficients and compare the different computational approaches.

Computational evidence for stable inorganic fullerene-like structures of ceramic and semiconductor materials

Theoretical electronic structure techniques have become an indispensible and powerful means for predicting molecular properties and designing new materials. Based on a density functional approach and guided by geometric considerations we provide evidence for some specific inorganic fullerene-like cage molecules of ceramic and semiconductor materials which exhibit high energetic stability and point group symmetry as well as nearly perfect spherical shape.

Theoretical study of stationary points of the MgSiO3 molecule

Structural properties of energetically low-lying stationary points of the MgSiO3 molecular system have been investigated by theoretical density functional techniques. A large number of singlet and triplet structures representing local minima of the neutral MgSiO3 molecule are completely characterised. The energetically lowest of these minima is a singlet state of planar kite-shaped C2v symmetry. The system equally possesses a variety of stable charged species of which the respectively lowest in energy is presented. We report energies, equilibrium geometric parameters, selected harmonic vibrational wave numbers along with corresponding absorption coefficients. Stability and geometric aspects are compared to the molecules Si2O3 and Mg2O3, as well as to the isoelectronic Al2O3 molecular system.

Sphericity: a geometric approach to the internal rotation of C2H6, H2O2, and N2H4

Abstract From a pure geometric point of view a three-dimensional molecular configuration can be considered to be a polyhedral skeleton. Based on the convex hull of the polyhedron it is possible to define a sphericity measure for the enclosing framework. This sphericity function which may be expressed in spatial coordinates is capable to mirror information about the structural characteristics of a molecular arrangement that habitually can only be arrived at by quantum mechanical computations. This concept is applied to the well-known internal rotation process of C2H6, H2O2, and N2H4.