128 research outputs found
Variational Monte Carlo for spin-orbit interacting systems
Recently, a diffusion Monte Carlo algorithm was applied to the study of spin
dependent interactions in condensed matter. Following some of the ideas
presented therein, and applied to a Hamiltonian containing a Rashba-like
interaction, a general variational Monte Carlo approach is here introduced that
treats in an efficient and very accurate way the spin degrees of freedom in
atoms when spin orbit effects are included in the Hamiltonian describing the
electronic structure. We illustrate the algorithm on the evaluation of the
spin-orbit splittings of isolated carbon and lead atoms. In the case of the
carbon atom, we investigate the differences between the inclusion of spin-orbit
in its realistic and effective spherically symmetrized forms. The method
exhibits a very good accuracy in describing the small energy splittings,
opening the way for a systematic quantum Monte Carlo studies of spin-orbit
effects in atomic systems.Comment: 7 pages, 0 figure
Recent progress on the accurate determination of the equation of state of neutron and nuclear matter
The problem of accurately determining the equation of state of nuclear and
neutron matter at density near and beyond saturation is still an open
challenge. In this paper we will review the most recent progress made by means
of Quantum Monte Carlo calculations, which are at present the only ab-inito
method capable to treat a sufficiently large number of particles to give
meaningful estimates depending only on the choice of the nucleon-nucleon
interaction. In particular, we will discuss the introduction of
density-dependent interactions, the study of the temperature dependence of the
equation of state, and the possibility of accurately studying the effect of the
onset of hyperons by developing an accurate hyperon-nucleon and
hyperon-nucleon-nucleon interaction.Comment: 3 figures, 1 table, to appear in the Proceedings of "XIII Convegno di
Cortona su Problemi di Fisica Nucleare Teorica", Cortona (Italy), April 6-8,
201
Correlation Induced Inhomogeneity in Circular Quantum Dots
Properties of the "electron gas" - in which conduction electrons interact by
means of Coulomb forces but ionic potentials are neglected - change
dramatically depending on the balance between kinetic energy and Coulomb
repulsion. The limits are well understood. For very weak interactions (high
density), the system behaves as a Fermi liquid, with delocalized electrons. In
contrast, in the strongly interacting limit (low density), the electrons
localize and order into a Wigner crystal phase. The physics at intermediate
densities, however, remains a subject of fundamental research. Here, we study
the intermediate-density electron gas confined to a circular disc, where the
degree of confinement can be tuned to control the density. Using accurate
quantum Monte Carlo techniques, we show that the electron-electron correlation
induced by an increase of the interaction first smoothly causes rings, and then
angular modulation, without any signature of a sharp transition in this density
range. This suggests that inhomogeneities in a confined system, which exist
even without interactions, are significantly enhanced by correlations.Comment: final version, modified introduction and clarifications, 4 page
Two ground-state modifications of quantum-dot beryllium
Exact electronic properties of a system of four Coulomb-interacting
two-dimensional electrons in a parabolic confinement are reported. We show that
degenerate ground states of this system are characterized by qualitatively
different internal electron-electron correlations, and that the formation of
Wigner molecule in the strong-interaction regime is going on in essentially
different ways in these ground states.Comment: 5 pages, incl 5 Figures and 2 Table
Assessment of Biological and Sanitary Condition of Alien Fish from a High-Mountain Lake (Cottian Alps)
This study aimed to assess the biological and sanitary conditions of alien fish in a high-mountain lake (Balma Lake) located in the Cottian Alps. A single fish sampling session (August 2018) using gillnets collected 90 specimens of brook trout (Salvelinus fontinalis). Sex and age were determined (59 females and 31 males, age class 0+ to 4+). Regression analysis showed no difference in total weight and total length between males and females (ANCOVA: F = 0.453; p = 0.954). The mean condition factor (Kmean) decreased with increasing age for males and females. Terrestrial insects were the main prey found in the fish stomachs. The parasitological exam was negative, and the bacteriological exam was positive for Carnobacterium maltaromaticum and C. divergens in 33% of specimens. The total mercury, cadmium, and lead concentration in muscle tissue was within the maximum limit established by the European Commission for human consumption. The brook trout population was found to be well structured; these findings may help local administrations in the implementation of eradication measures
Microscopic calculation of the equation of state of nuclear matter and neutron star structure
We present results for neutron star models constructed with a new equation of
state for nuclear matter at zero temperature. The ground state is computed
using the Auxiliary Field Diffusion Monte Carlo (AFDMC) technique, with
nucleons interacting via a semi-phenomenological Hamiltonian including a
realistic two-body interaction. The effect of many-body forces is included by
means of additional density-dependent terms in the Hamiltonian. In this letter
we compare the properties of the resulting neutron-star models with those
obtained using other nuclear Hamiltonians, focusing on the relations between
mass and radius, and between the gravitational mass and the baryon number.Comment: modified version with a slightly different Hamiltonian and
parametrization of the EO
Roto-vibrational spectrum and Wigner crystallization in two-electron parabolic quantum dots
We provide a quantitative determination of the crystallization onset for two
electrons in a parabolic two-dimensional confinement. This system is shown to
be well described by a roto-vibrational model, Wigner crystallization occurring
when the rotational motion gets decoupled from the vibrational one. The Wigner
molecule thus formed is characterized by its moment of inertia and by the
corresponding sequence of rotational excited states. The role of a vertical
magnetic field is also considered. Additional support to the analysis is given
by the Hartree-Fock phase diagram for the ground state and by the random-phase
approximation for the moment of inertia and vibron excitations.Comment: 10 pages, 8 figures, replaced by the published versio
Symmetry breaking and the random-phase approximation in small quantum dots
The random-phase approximation has been used to compute the properties of
parabolic two-dimensional quantum dots beyond the mean-field approximation.
Special emphasis is put on the ground state correlation energy, the symmetry
restoration and the role of the spurious modes within the random-phase
approximation. A systematics with the Coulombic interaction strength is
presented for the 2-electron dot, while for the 6- and 12-electron dots
selected cases are discussed. The validity of the random-phase approximation is
assessed by comparison with available exact results.Comment: 9 pages, 4 embedded + 6 gif Figs. Published versio
Diffusion Monte Carlo study of circular quantum dots
We present ground and excited state energies obtained from Diffusion Monte
Carlo (DMC) calculations, using accurate multiconfiguration wave functions, for
electrons () confined to a circular quantum dot. We analyze the
electron-electron pair correlation functions and compare the density and
correlation energies to the predictions of local spin density approximation
theory (LSDA). The DMC estimated change in electrochemical potential as
function of the number of electrons in the dot is compared to that from LSDA
and Hartree-Fock (HF) calculations.Comment: 7 pages, 4 eps figures. To be published in Phys. Rev. B, September
15th 2000. See erratum cond-mat/030571
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