Minimal mass-size of a stable 3He cluster

The minimal number of 3He atoms required to form a bound cluster has been estimated by means of a Diffusion Monte Carlo procedure within the fixed-node approximation. Several importance sampling wave functions have been employed in order to consider different shell-model configurations. The resulting upper bound for the minimal number is 32 atoms.Comment: 2 pages, no figure

Excitation spectra of a 3He impurity on 4He clusters

The diffusion Monte Carlo technique is used to calculate and analyze the excitation spectrum of a single 3He atom bound to a cluster with N 4He atoms, with the aim of establishing the most adequate filling ordering of single-fermion orbits to the mixed clusters with a large number of 3He atoms. The resulting ordering looks like the rotational spectrum of a diatomic molecule, being classified only by the angular momentum of the level, although vibrational-like excitations appear at higher energies for sufficiently large N

Translationally-invariant coupled-cluster method for finite systems

The translational invariant formulation of the coupled-cluster method is presented here at the complete SUB(2) level for a system of nucleons treated as bosons. The correlation amplitudes are solution of a non-linear coupled system of equations. These equations have been solved for light and medium systems, considering the central but still semi-realistic nucleon-nucleon S3 interaction.Comment: 16 pages, 2 Postscript figures, to be published in Nucl. Phys.

Excited states of 4He droplets

We study low-lying excited states of 4He clusters up to a cluster size of 40 atoms in a variational framework. The ansatz wave function combines two- and three-body correlations, coming from a translationally invariant configuration interaction description, and Jastrow-type short-range correlation. We have previously used this scheme to determine the ground-state energies of 4He and 3He clusters. Here we present an extension of this ansatz wave function having a good quantum angular momentum L. The variational procedure is applied independently to the cases with L = 0,2,4, and upper bounds for the corresponding energies are thus obtained. Moreover, centroid energies for L excitations are calculated through the use of sum rules. A comparison with previous calculations is also made.Fil: Guardiola, R.. Facultad de Física / Dpto de Física Atómica y Nuclear; EspañaFil: Navarro, J.. Csic - Univ. de Valencia / Inst. de Física Corpuscular; EspañaFil: Portesi, Mariela Adelina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentin

Excitation levels and magic numbers of small para-Hydrogen clusters (N≤40 \le 40)

The excitation energies of parahydrogen clusters have been systematically calculated by the diffusion Monte Carlo technique in steps of one molecule from 3 to 40 molecules. These clusters possess a very rich spectra, with angular momentum excitations arriving up to L=13 for the heavier ones. No regular pattern can be guessed in terms of the angular momenta and the size of the cluster. Clusters with N=13 and 36 are characterized by a peak in the chemical potential and a large energy gap of the first excited level, which indicate the magical character of these clusters. From the calculated excitation energies the partition function has been obtained, thus allowing for an estimate of thermal effects. An enhanced production is predicted for cluster sizes N=13, 31 and 36, in agreement with experiment.Comment: 20 pages, 4 figur

The spectra of mixed 3^3He-4^4He droplets

The diffusion Monte Carlo technique is used to calculate and analyze the excitation spectrum of $^3$He atoms bound to a cluster of $^4$He atoms, by using a previously determined optimum filling of single-fermion orbits with well defined orbital angular momentum $L$, spin $S$ and parity quantum numbers. The study concentrates on the energies and shapes of the three kinds of states for which the fermionic part of the wave function is a single Slater determinant: maximum $L$ or maximum $S$ states within a given orbit, and fully polarized clusters. The picture that emerges is that of systems with strong shell effects whose binding and excitation energies are essentially determined over configuration at fixed number of particles and spin, i.e., by the monopole properties of an effective Hamiltonian.Comment: 14 pages, 15 figure

Translationally invariant treatment of pair correlations in nuclei: II. Tensor correlations

We study the extension of our translationally invariant treatment of few-body nuclear systems to include tensor forces and correlations. It is shown that a direct application of our method is not as successful for realistic V6 interactions as our previous results for V4 potentials suggested. We investigate the cause in detail for the case of $^4$He, and show that a combination of our method with that of Jastrow-correlated wave functions seems to be a lot more powerful, thereby suggesting that for mildly to strongly repulsive forces such a hybrid procedure may be an appropriate description.Comment: 19 pages, 3 ps figures. uses elsart, graphicx, amssym

Two-dimensional molecular para-hydrogen and ortho-deuterium at zero temperature

We study molecular para-hydrogen (p-${\rm H_{2}}$) and ortho-deuterium (o-${\rm D_{2}}$) in two dimensions and in the limit of zero temperature by means of the diffusion Monte Carlo method. We report energetic and structural properties of both systems like the total and kinetic energy per particle, radial pair distribution function, and Lindemann's ratio in the low pressure regime. By comparing the total energy per particle as a function of the density in liquid and solid p-${\rm H_{2}}$, we show that molecular para-hydrogen, and also ortho-deuterium, remain solid at zero temperature. Interestingly, we assess the quality of three different symmetrized trial wave functions, based on the Nosanow-Jastrow model, in the p-${\rm H_{2}}$ solid film at the variational level. In particular, we analyze a new type of symmetrized trial wave function which has been used very recently to describe solid $^{4}$He and found that also characterizes hydrogen satisfactorily. With this wave function, we show that the one-body density matrix $\varrho_{1} (r)$ of solid p-${\rm H_{2}}$ possesses off-diagonal long range order, with a condensate fraction that increases sizably in the negative pressure regime.Comment: 11 pages, 9 figure

Superficial oscillation as an identifier of phenomena governing dynamics of solid-gas fluidized systems

The evolution of the volume of a fluidized bed solid–gas over time is measured by the oscillation of its surface. It is assumed that the system is governed by the pressure gradient between the plenum and the surface; the latter is considered as the reference. The surface oscillation is measured with a laterally located CCD video camera such that it monitors the flattest portion of the surface and records its coordinates. Simultaneously obtain all the phenomena that regulate the hydrodynamics of the bed, the entering bubbles, coalesce, split, increase their volume adiabatically, and explode on the surface. The gas flow and the weight of fluidized material are studied. The time series of the surface oscillation is analysed in the frequency domain and the phase space. The frequencies obtained are approximately between 0.6 Hz and 1.8 Hz. The entropy values behaves linearly proportional to the total number of bubbles