Search

The search for the ground state structures of Boron clusters has been a difficult computational task due to the unique metalloid nature of Boron atom. Previous research works had overcome the problem in the search of the Boron ground-state structures by adding symmetry constraints prior to the process of locating the local minima in the potential energy surface (PES) of the Boron clusters. In this work, we shown that, with the deployment of a novel computational approach that incorporates density functional theory (DFT) into a guided global optimization search algorithm based on basin-hopping, it is possible to directly locate the local minima of small Boron clusters in the PES at the DFT level. The ground-state structures search algorithm as proposed in this work is initiated randomly and needs not a priori symmetry constraint artificially imposed throughout the search process. Small sized Boron clusters so obtained compare well to the results obtained by similar calculations in the literature. The electronic properties of each structures obtained are calculated within the DFT framework. [ABSTRACT FROM AUTHOR]

Based on our new calculations of its structure, we discuss the possibility for the H3- ion to be formed and observed in cold and dense interstellar medium in an environment with a large fraction of ionized molecular hydrogen. The detection the H- ion would be a probe for the presence of H- in the interstellar medium. [ABSTRACT FROM AUTHOR]

Structure and dynamics of HeI2 van der Waals (vdW) complex are analyzed from first principles. Ab initio technology, at CCSD(T) and MRCI level of theories, was employed for constructing potential energy surfaces of the ground and excited electronic states, and a full quantum mechanical treatment for studying its dynamics was applied. Spectroscopy in the visible region involving an electronic B-X transition offers the possibility of a detailed comparison with the theoretical results. A description of the ab initio approach adopted, together with its limitations, and further improvements are discussed. [ABSTRACT FROM AUTHOR]

Disilicon hydrides as candidates of interstellar molecules have been studied employing density functional and coupled cluster quantum chemical methods. Potential energy surfaces of Si2H and Si2H2 in the electronic ground state reveal that several isomeric structures are energetically well separated. This means that these isomers can be distinguished in low-temperature conditions such as the interstellar medium due to the disfavor of their inter-conversions. Two nearly degenerate states exist for cyclic structures of Si2H that both can be possible isomers. In the case of Si2H2, four isomeric structures are well separated by energy barriers for isomerization processes between them. We have also examined potential energy surfaces in the lowest excited state for the Si2H and Si2H2 species and found that the energies of several isomeric species in the ground state are very close to their energies in the lowest excited states. The reactivity of Si2H and Si2H2 with hydrogen atom is examined and possible formation mechanisms of Si2H and Si2H2 molecules via neutral-neutral reactions are discussed as astrophysical implications. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The potential energy surfaces (PES) for the singlet and triplet H2O2 molecular system were studied by using the CASSCF, CASPT2, QCISD, QCISD(T), and CCSD(T) methods with the aug-cc-pVDZ, aug-cc-pVTZ, and 6-311+G(3df,2p) basis sets. The CASSCF and CASPT2 results show some significant differences from the QCISD, QCISD(T), and CCSD(T) calculations. The QCISD(T)//QCISD and CCSD(T)//QCISD calculations were found to be suitable for examining most of the species and reaction paths on the H2O2 PES except for a few open shell species which have a multi-reference character. The CASSCF and CASPT2 methods were found to be better suited for treating these open shell species. Consistent with previous theoretical and experimental work we find the hydrogen abstraction reaction 1O + H2O → 2OH + 2OH to have a small or no energy barrier suggesting this pathway may have relevance to the astrochemical formation of hydrogen peroxide in an extraterrestrial environment. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Various valleys of the deformation potential energy surface relevant to fission and fusion processes have been investigated within the same Skyrme-Hartree-Fock plus BCS microscopic model in the A = 70 and A > 220 mass regions. The available experimental fission barrier heights of actinides are reproduced within a rms error of 1.5 MeV whereas the conditional barriers of the considered light nucleus are overestimated by about 10 MeV. The fission paths describing the descent from saddle to scission have been found consistent with the results obtained with the Gogny force used in the Hartree-Fock-Bogolyubov approach and in agreement with the experimental mass distributions. In general, the valleys corresponding to very asymmetric separated shapes (close to the Pb plus light partner configuration) are in agreement with the most favorable target-projectile combinations in cold fusion reactions experimentally used to form such compound nuclei. The deduced fusion barrier heights have been found about 10 MeV lower than those obtained within the Extended Thomas Fermi model. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Spectra of Rg 1S0→3,1P1 transitions in Rg/M mixtures, Rg=Xe,Kr, and M=CF4, C2F6, in the Vac UV region have been recorded at higher resolution. Potentials of Rg-M collisional complexes have been computed using the atom-bond pairwise additive formalism. Experimental and simulated line shapes of 1S0→3,1P1 transitions are compared and discussed. [ABSTRACT FROM AUTHOR]

Even-even nuclei in the A ∼100 mass region are investigated within the framework of the interacting boson model-1 (IBM-1). The parametrization established on the basis of known elements is then used to predict properties of the unknown. This paper includes the predicted energy spectra and the potential energy surface obtained from the IBM-1 hamiltonian in the classical limit. [ABSTRACT FROM AUTHOR]