Bonding in doped gallium nanoclusters: Insights from regional DFT

The molecular nature (Ga2)n of gallium makes this an interesting metal to investigate for the development of novel nano-materials. However, establishment of a targeted approach to manipulating the properties of gallium clusters requires a detailed understanding of how doping affects the bonding in these species. In this study, the bonding of gallium nanoclusters has been investigated using electron deformation densities and Regional Density Functional Theory (RDFT). Bonding throughout Ga12X clusters is generally intermediate between covalent and metallic. However, the presence of Ga2 subunits is clearly identified in clusters with endohedral dopants (Ga12X, X = Al, Si, P, Ga, Ge, As). Although there is evidence of Ga2 subunits in exohedral doped clusters, localised bonding to the dopant generally leads to significant disruption to the cluster framework. Maps of electronic chemical potential provide understanding for the observed differences in regioselectivity for hydrogen adsorption

The Cosmic Neutrino Background and the Age of the Universe

We discuss the cosmological degeneracy between the age of the Universe, the Hubble parameter and the effective number of relativistic particles N_eff. We show that independent determinations of the Hubble parameter H(z) as those recently provided by Simon,Verde, Jimenez (2006), combined with other cosmological data sets can provide the most stringent constraint on N_eff, yielding N_eff=3.7 (-1.2) (+1.1) at 95% confidence level. A neutrino background is detected with high significance: N_eff >1.8 at better than 99% confidence level. Constraints on the age of the universe in the framework of an extra background of relativistic particles are improved by a factor 3.Comment: JCAP, in pres

Electronic stress tensor analysis of hydrogenated palladium clusters

We study the chemical bonds of small palladium clusters Pd_n (n=2-9) saturated by hydrogen atoms using electronic stress tensor. Our calculation includes bond orders which are recently proposed based on the stress tensor. It is shown that our bond orders can classify the different types of chemical bonds in those clusters. In particular, we discuss Pd-H bonds associated with the H atoms with high coordination numbers and the difference of H-H bonds in the different Pd clusters from viewpoint of the electronic stress tensor. The notion of "pseudo-spindle structure" is proposed as the region between two atoms where the largest eigenvalue of the electronic stress tensor is negative and corresponding eigenvectors forming a pattern which connects them.Comment: 22 pages, 13 figures, published online, Theoretical Chemistry Account

The Hubble constant and dark energy from cosmological distance measures

We study how the determination of the Hubble constant from cosmological distance measures is affected by models of dark energy and vice versa. For this purpose, constraints on the Hubble constant and dark energy are investigated using the cosmological observations of cosmic microwave background, baryon acoustic oscillations and type Ia suprenovae. When one investigates dark energy, the Hubble constant is often a nuisance parameter, thus it is usually marginalized over. On the other hand, when one focuses on the Hubble constant, simple dark energy models such as a cosmological constant and a constant equation of state are usually assumed. Since we do not know the nature of dark energy yet, it is interesting to investigate the Hubble constant assuming some types of dark energy and see to what extent the constraint on the Hubble constant is affected by the assumption concerning dark energy. We show that the constraint on the Hubble constant is not affected much by the assumption for dark energy. We furthermore show that this holds true even if we remove the assumption that the universe is flat. We also discuss how the prior on the Hubble constant affects the constraints on dark energy and/or the curvature of the universe.Comment: 45 pages, 15 figure

Neutrino mass constraint from CMB and its degeneracy with other cosmological parameters

We show that the cosmic microwave background (CMB) data of WMAP can give subelectronvolt limit on the neutrino mass: m_nu < 0.63 eV (95% CL). We also investigate its degeneracy with other cosmological parameters. In particular, we show the Hubble constant derived from the WMAP data decreases considerably when the neutrino mass is a few times 0.1 eV.Comment: 3 pages, 2 figures, prepared for the TAUP2007 Proceeding