9,859 research outputs found
Ground State Spin Structure of Strongly Interacting Disordered 1D Hubbard Model
We study the influence of on-site disorder on the magnetic properties of the
ground state of the infinite U 1D Hubbard model. We find that the ground state
is not ferromagnetic. This is analyzed in terms of the algebraic structure of
the spin dependence of the Hamiltonian. A simple explanation is derived for the
1/N periodicity in the persistent current for this model.Comment: 3 pages, no figure
Cluster-variation approximation for a network-forming lattice-fluid model
We consider a 3-dimensional lattice model of a network-forming fluid, which
has been recently investigated by Girardi and coworkers by means of Monte Carlo
simulations [J. Chem. Phys. \textbf{126}, 064503 (2007)], with the aim of
describing water anomalies. We develop an approximate semi-analytical
calculation, based on a cluster-variation technique, which turns out to
reproduce almost quantitatively different thermodynamic properties and phase
transitions determined by the Monte Carlo method. Nevertheless, our calculation
points out the existence of two different phases characterized by long-range
orientational order, and of critical transitions between them and to a
high-temperature orientationally-disordered phase. Also, the existence of such
critical lines allows us to explain certain ``kinks'' in the isotherms and
isobars determined by the Monte Carlo analysis. The picture of the phase
diagram becomes much more complex and richer, though unfortunately less
suitable to describe real water.Comment: 10 pages, 9 figures, submitted to J. Chem. Phy
Revisiting waterlike network-forming lattice models
In a previous paper [J. Chem. Phys. 129, 024506 (2008)] we studied a 3
dimensional lattice model of a network-forming fluid, recently proposed in
order to investigate water anomalies. Our semi-analytical calculation, based on
a cluster-variation technique, turned out to reproduce almost quantitatively
several Monte Carlo results and allowed us to clarify the structure of the
phase diagram, including different kinds of orientationally ordered phases.
Here, we extend the calculation to different parameter values and to other
similar models, known in the literature. We observe that analogous ordered
phases occur in all these models. Moreover, we show that certain "waterlike"
thermodynamic anomalies, claimed by previous studies, are indeed artifacts of a
homogeneity assumption made in the analytical treatment. We argue that such a
difficulty is common to a whole class of lattice models for water, and suggest
a possible way to overcome the problem.Comment: 13 pages, 12 figure
Glassy states in lattice models with many coexisting crystalline phases
We study the emergence of glassy states after a sudden cooling in lattice
models with short range interactions and without any a priori quenched
disorder. The glassy state emerges whenever the equilibrium model possesses a
sufficient number of coexisting crystalline phases at low temperatures,
provided the thermodynamic limit be taken before the infinite time limit. This
result is obtained through simulations of the time relaxation of the standard
Potts model and some exclusion models equipped with a local stochastic dynamics
on a square lattice.Comment: 12 pages, 4 figure
Consequences of wall stiffness for a beta-soft potential
Modifications of the infinite square well E(5) and X(5) descriptions of
transitional nuclear structure are considered. The eigenproblem for a potential
with linear sloped walls is solved. The consequences of the introduction of
sloped walls and of a quadratic transition operator are investigated.Comment: RevTeX 4, 8 pages, as published in Phys. Rev.
A simple description of the states and in
A sixth-order quadrupole boson Hamiltonian is used to describe 26 states
and 67 states which have been recently identified in .
Two closed expressions are alternatively used for energy levels. One
corresponds to a semi-classical approach while the other one represents the
exact eigenvalue of the model Hamiltonian. The semi-classical expression
involves four parameters, while the exact eigenvalue is determined by five
parameters. In each of the two descriptions a least square fit procedure is
adopted.
Both expressions provide a surprisingly good agreement with the experimental
data.Comment: 9 pages, 5 figure
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