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Model Cluster (model + cluster)
Selected AbstractsTotal cluster energy calculation of lithium ion conductors by the DV-X, methodINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 12 2009Y. Kowada Abstract Recently, several programs for the total cluster energy calculation have been developed in the DV-X, method. In this study, we have calculated and compared total cluster energies of several diatomic molecules and model clusters of ionic conductors. The total cluster energies of diatomic molecules are minimum near the equilibrium atomic distance of each molecule though the absolute value of the total cluster energy was slightly different from each other. In the case of the model cluster of the Li3N crystal, which is one of the typical Li ion conductors, we have obtained the energy change as a function of the site during the movement of a Li ion. The energy change with the movement of the Li ion along the conduction path was considerably smaller than along other paths, consistent with the results by the band calculation and experiments. The total cluster energy calculation method was useful enough for the discussion of the cluster energy. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] DFT study for the heterojunction effect in the precious metal clustersINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2008Mitsutaka Okumura Abstract In the case of the precious metal catalysts, the precious metal nanoparticles deposited on the several supports exhibit extremely high-catalytic activity for many catalytic reactions. The boundary region between the nanoparticles and the support is one of the active sites in these catalysts. Moreover, the core/shell-type bimetallic nanoparticles also show the high-catalytic activities for several catalytic reactions. In these systems, the electronic states of the surfaces in the clusters are modified by the heterojunction between the two different compositions. Therefore, we investigate the heterojunction effect in these model catalysts, such as precious metal core/shell clusters and Pd supported on single-wall carbon nanotube model cluster, using hybrid density functional theory. From the calculation results, we find that the charge transfer interactions and the variation of the ground spin states in the metal clusters are the characteristics induced by the heterojunction in these model systems. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Energy density analysis of cluster size dependence of surface,molecule interactions (II): Formate adsorption onto a Cu(111) surfaceJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 8 2006Hiromi Nakai Abstract Adsorption of formate (HCOO) onto a Cu(111) surface has been treated theoretically using 18 kinds of Cun (6 , n , 56) clusters. The energy density analysis (EDA) proposed by Nakai has been adopted to examine surface,molecule interactions for different cluster sizes. EDA results for the largest model cluster Cu56 have shown that the adsorption-induced energy density variation in Cu atoms decays with distance from the adsorption site. Analysis of this decay, which can be carried out using the EDA technique, is important because it enables verification of the reliability of the model cluster used. In the case of formate adsorption onto the Cu(111) surface, it is found that at least a four-layer model cluster is necessary to treat the surface,molecule interaction with chemical accuracy. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 917,925, 2006 [source] Total cluster energy calculation of lithium ion conductors by the DV-X, methodINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 12 2009Y. Kowada Abstract Recently, several programs for the total cluster energy calculation have been developed in the DV-X, method. In this study, we have calculated and compared total cluster energies of several diatomic molecules and model clusters of ionic conductors. The total cluster energies of diatomic molecules are minimum near the equilibrium atomic distance of each molecule though the absolute value of the total cluster energy was slightly different from each other. In the case of the model cluster of the Li3N crystal, which is one of the typical Li ion conductors, we have obtained the energy change as a function of the site during the movement of a Li ion. The energy change with the movement of the Li ion along the conduction path was considerably smaller than along other paths, consistent with the results by the band calculation and experiments. The total cluster energy calculation method was useful enough for the discussion of the cluster energy. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Star cluster ecology , V. Dissection of an open star cluster: spectroscopyMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2004Simon F. Portegies Zwart ABSTRACT We have modelled in detail the evolution of rich open star clusters such as NGC 2516, NGC 2287, Pleiades, Praesepe, Hyades, NGC 2660 and 3680, using simulations that include stellar dynamics as well as the effects of stellar evolution. The dynamics is modelled via direct N -body integration, while the evolution of single stars and binaries is followed through the use of fitting formulae and recipes. The feedback of stellar and binary evolution on the dynamical evolution of the stellar system is taken into account self-consistently. Our model clusters dissolve in the tidal field of the Galaxy in a time-span of the order of a billion years. The rate of mass loss is rather constant, ,1 M, per million years. The binary fraction at first is nearly constant in time, then increases slowly near the end of a cluster's lifetime. For clusters which are more than about 108 yr old the fractions of stars in the form of binaries, giants and merger products in the inner few core radii are considerably higher than in the outer regions, beyond the cluster's half-mass radius. When stars with masses ,2 M, escape from the cluster, they tend to do so with velocities higher than average. The stellar merger rate in our models is roughly one per 30 million years. Most mergers are the result of unstable mass transfer in close binaries (,70 per cent), but a significant minority are caused by direct encounters between single and binary stars. While most mergers occur within the cluster core, even beyond the half-mass radius stellar mergers occasionally take place. We notice a significant birth rate of X-ray binaries, most containing a white dwarf as the mass acceptor. We also find one high-mass X-ray binary with a neutron-star accretor. If formed and retained, black holes participate in many (higher-order) encounters in the cluster centre, resulting in a large variety of exotic binaries. The persistent triple and higher-order systems formed in our models by dynamical encounters between binaries and single stars are not representative for the multiple systems observed in the Galactic disc. We conclude that the majority of multiples in the disc probably formed when the stars were born, rather than through later dynamical interactions. [source] | ||||||||||