Trapped Fermi gases

We study the properties of a spin-polarized Fermi gas in a harmonic trap, using the semiclassical (Thomas-Fermi) approximation. Universal forms for the spatial and momentum distributions are calculated, and the results compared with the corresponding properties of a dilute Bose gas.Comment: 6 pages, LaTex, revtex, epsf, submitted to Phys. Rev. A, 6 December 199

A diffusion Monte Carlo study of small para-Hydrogen clusters

Ground state energies and chemical potentials of parahydrogen clusters are calculated from 3 to 40 molecules using the diffusion Monte Carlo technique with two different pH2-pH2 interactions. This calculation improves a previous one by the inclusion of three-body correlations in the importance sampling, by the time step adjustement and by a better estimation of the statistical errors. Apart from the cluster with 13 molecules, no other magic clusters are predicted, in contrast with path integral Monte Carlo results

Variational Monte Carlo study of the ground state properties and vacancy formation energy of solid para-H2 using a shadow wave function

A Shadow Wave Function (SWF) is employed along with Variational Monte Carlo techniques to describe the ground state properties of solid molecular para-hydrogen. The study has been extended to densities below the equilibrium value, to obtain a parameterization of the SWF useful for the description of inhomogeneous phases. We also present an estimate of the vacancy formation energy as a function of the density, and discuss the importance of relaxation effects near the vacant site

Coupled Ripplon-Plasmon Modes in a Multielectron Bubble

In multielectron bubbles, the electrons form an effectively two-dimensional layer at the inner surface of the bubble in helium. The modes of oscillation of the bubble surface (the ripplons) are influenced by the charge redistribution of the electrons along the surface. The dispersion relation for these charge redistribution modes (`longitudinal plasmons') is derived and the coupling of these modes to the ripplons is analysed. We find that the ripplon-plasmon coupling in a multielectron bubble differs markedly from that of electrons a flat helium surface. An equation is presented relating the spherical harmonic components of the charge redistribution to those of the shape deformation of the bubble.Comment: 8 pages, 1 figure, E-mail addresses: [email protected], [email protected], [email protected], [email protected]

A non trivial extension of the two-dimensional Ising model: the d-dimensional "molecular" model

A recently proposed molecular model is discussed as a non-trivial extension of the Ising model. For d=2 the two models are shown to be equivalent, while for d>2 the molecular model describes a peculiar second order transition from an isotropic high temperature phase to a low-dimensional anisotropic low temperature state. The general mean field analysis is compared with the results achieved by a variational Migdal-Kadanoff real space renormalization group method and by standard Monte Carlo sampling for d=3. By finite size scaling the critical exponent has been found to be 0.44\pm 0.02 thus establishing that the molecular model does not belong to the universality class of the Ising model for d>2.Comment: 25 pages, 5 figure

H2 in the interstitial channels of nanotube bundles

The equation of state of H2 adsorbed in the interstitial channels of a carbon nanotube bundle has been calculated using the diffusion Monte Carlo method. The possibility of a lattice dilation, induced by H2 adsorption, has been analyzed by modeling the cohesion energy of the bundle. The influence of factors like the interatomic potentials, the nanotube radius and the geometry of the channel on the bundle swelling is systematically analyzed. The most critical input is proved to be the C-H2 potential. Using the same model than in planar graphite, which is expected to be also accurate in nanotubes, the dilation is observed to be smaller than in previous estimations or even inexistent. H2 is highly unidimensional near the equilibrium density, the radial degree of freedom appearing progressively at higher densities.Comment: Accepted for publication in PR