Grain formation and dynamical atmosphere

Dust forming systems, in which a phase transition between the gas phase and the solid state takes place, are seriously affected by the presence of dust, which causes tight, non-linear interactions between various physical and chemical processes. As a consequence, the dynamics of, e.g., a stellar atmosphere and the formation of dust grains are inseparably connected. Chemical conditions, dust formation, and dust-induced instabilities in such non-linearly coupled systems as well as some implications regarding stellar evolution are discussed

A density functional study of small Al

We report thermodynamic properties of small aluminium oxide clusters of mixed stoichiometric ratio AlxOy $(x,y=1{-}4)$. The rigid rotator-harmonic oscillator approximation is used to calculate the partition function as it is generally applied in thermodynamic studies of polyatomic molecules. The molecular data used to set up the partition functions were computed by density functional techniques employing the BP86 gradient corrected exchange correlation functional. Thereby, the results of three species viz. AlO4, Al4O2, and Al4O3 previously not reported in the literature are included in this study. Equilibrium geometric parameters, energies, selected harmonic vibrational wave numbers of energetically low–lying stationary points are presented along with corresponding absorption coefficients. The resulting thermodynamic functions of aluminium oxides are consistent with the JANAF thermochemical data compilation. These functions are used to determine the temperature dependent chemical equilibrium partial pressure distributions for different aluminium to oxygen ratios

Ab initio studies of stationary points of the Al

We report a theoretical ab initio investigation on energetically low-lying stationary points of the Al2O3 molecular system. The calculations were performed at the Hartree-Fock (HF) and second-order Møller-Plesset (MP2) frozen core level of approximation using the standard 6-31G(d) basis set. Several isomeric singlet as well as higher spin states of Al2O3 which lie close to each other within an energy range of about 8 eV (at MP2) are characterised. The lowest of these stationary points is in fact a triplet state of planar $\rm C_{2v}$ symmetry. It is by 0.08 eV (MP2) lower than the often discussed linear $\rm D_{\rm \infty h}$ singlet state. Atomisation energies for all species are quite large showing that the system is strongly bound. Energies, harmonic vibrational modes, and geometric parameters are compared with the results of earlier work by Solomonik and Sliznev [CITE], Nemukhin and Weinhold [CITE], Andrews et al. [CITE] and Desai et al. [CITE]. Based on our calculations we give a tentative assignment of some selected vibrational wave numbers and an interpretation of some features of the photoelectron spectrum