0000000000273442
AUTHOR
Jesús Navarro Faus
Microscopic study of He2-SF6 trimers
The He2-SF6 trimers, in their different He isotopic combinations, are studied in the framework of both the correlated Jastrow approach and the correlated hyperspherical harmonics (CHH) expansion method. The energetics and structure of the He-SF6 dimers are analyzed, and the existence of a characteristic rotational band in the excitation spectrum is discussed, as well as the isotopic differences. The binding energies and the spatial properties of the trimers, in their ground and lowest lying excited states, obtained by the Jastrow ansatz are in excellent agreement with the results of the converged CHH expansion. The introduction of the He-He correlation makes all trimers bound by largely sup…
High-quality variational wave functions for small He-4 clusters
We report a variational calculation of ground state energies and radii for 4He_N droplets (3 \leq N \leq 40), using the atom-atom interaction HFD-B(HE). The trial wave function has a simple structure, combining two- and three-body correlation functions coming from a translationally invariant configuration-interaction description, and Jastrow-type short-range correlations. The calculated ground state energies differ by around 2% from the diffusion Monte Carlo results.
Excitation spectra of a He-3 impurity on He-4 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.
Dificultades en la enseñanza/aprendizaje de la física cuántica
Abstract We have elaborated a questionnaire about some selected basic concepts on Modern Physics, We have then analysed the students comprehension level on Quantum Physics before they follow this matter in the 3er year of Physics studies. Once this course has been completed. the evolution of the previous misconceptions is studied. We conclude that a teaching which considers previous misconceptions results in a sensitive improvement. However, we also detect the persistence of a few misconceptions acquired during the non-university teaching.
Two-dimensional clusters of liquid He-4
The binding energies of two-dimensional clusters (puddles) of 4He are calculated in the framework of the diffusion Monte Carlo method. The results are very well fitted by a mass formula in powers of x=N−1/2, where N is the number of particles. The analysis of the mass formula allows for the extraction of the line tension, which turns out to be 0.121 K/A. Sizes and density profiles of the puddles are also reported.
Monte Carlo Calculations for Liquid $^4$He at Negative Pressure
A Quadratic Diffusion Monte Carlo method has been used to obtain the equation of state of liquid $^4$He including the negative pressure region down to the spinodal point. The atomic interaction used is a renewed version (HFD-B(HE)) of the Aziz potential, which reproduces quite accurately the features of the experimental equation of state. The spinodal pressure has been calculated and the behavior of the sound velociy around the spinodal density has been analyzed.
Ca impurity in small mixed He-4-He-3 clusters
The structure of small mixed helium clusters doped with one calcium atom has been determined within the diffusion Monte Carlo framework. The results show that the calcium atom sits at the He-4-He-3 interface. This is in agreement with previous studies, both experimental and theoretical, performed for large clusters. A comparison between the results obtained for the largest cluster we have considered for each isotope shows a clear tendency of the Ca atom to reside in a deep dimple at the surface of the cluster for He-4 clusters, and to become fully solvated for He-3 clusters. We have calculated the absorption spectrum of Ca around the 4s4p <- 4s(2) transition and have found that it is bluesh…
Magic numbers, excitation levels, and other properties of small neutral math clusters (N < 50)
The ground-state energies and the radial and pair distribution functions of neutral math clusters are systematically calculated by the diffusion Monte Carlo method in steps of one math atom from 3 to 50 atoms. In addition the chemical potential and the low-lying excitation levels of each cluster are determined with high precision. These calculations reveal that the “magic numbers” observed in experimental math cluster size distributions, measured for free jet gas expansions by nondestructive matter-wave diffraction, are not caused by enhanced stabilities. Instead they are explained in terms of an enhanced growth due to sharp peaks in the equilibrium concentrations in the early part of the e…