822 research outputs found
Realistic simulations of Au(100): Grand Canonical Monte Carlo and Molecular Dynamics
The large surface density changes associated with the (100) noble metals
surface hex-reconstruction suggest the use of non-particle conserving
simulation methods. We present an example of a surface Grand Canonical Monte
Carlo applied to the transformation of a square non reconstructed surface to
the hexagonally covered low temperature stable Au(100). On the other hand,
classical Molecular Dynamics allows to investigate microscopic details of the
reconstruction dynamics, and we show, as an example, retraction of a step and
its interplay with the surface reconstruction/deconstruction mechanism.Comment: 9 pages, 5 figures, accepted for publication in Surf. Rev. and
Letters (ICSOS-6
Multiple jumps and vacancy diffusion in a face-centered cubic metal
The diffusion of monovacancies in gold has been studied by computer
simulation. Multiple jumps have been found to play a central role in the atomic
dynamics at high temperature, and have been shown to be responsible for an
upward curvature in the Arrhenius plot of the diffusion coefficient.
Appropriate saddle points on the potential energy surface have been found,
supporting the interpretation of vacancy multiple jumps as distinct migration
mechanisms.Comment: 16 page
Bent surface free energy differences from simulation
We present a calculation of the change of free energy of a solid surface upon
bending of the solid. It is based on extracting the surface stress through a
molecular dynamics simulation of a bent slab by using a generalized stress
theorem formula, and subsequent integration of the stress with respect to
strain as a function of bending curvature. The method is exemplified by
obtaining and comparing free energy changes with curvature of various
reconstructed Au(001) surfaces.Comment: 14 pages, 2 figures, accepted for publication in Surface Science
(ECOSS-19
Melting and nonmelting of solid surfaces and nanosystems
We present an extensive but concise review of our present understanding,
largely based on theory and simulation work from our group, on the equilibrium
behavior of solid surfaces and nanosystems close to the bulk melting point. In
the first part we define phenomena, in particular surface melting and
nonmelting, and review some related theoretical approaches, from heuristic
theories to computer simulation. In the second part we describe the surface
melting/nonmelting behavior of several different classes of solids, ranging
from van der Waals crystals, to valence semiconductors, to ionic crystals and
metals. In the third part, we address special cases such as strained solids,
the defreezing of glass surfaces, and rotational surface melting. Next, we
digress briefly to surface layering of a liquid metal, possibly leading to
solid-like or hexatic two dimensional phases floating on the liquid. In the
final part, the relationship of surface melting to the premelting of
nanoclusters and nanowires is reviewed.Comment: 54 pages, 26 figure
On critical phases in anisotropic spin-1 chains
Quantum spin-1 chains may develop massless phases in presence of Ising-like
and single-ion anisotropies. We have studied c=1 critical phases by means of
both analytical techniques, including a mapping of the lattice Hamiltonian onto
an O(2) nonlinear sigma model, and a multi-target DMRG algorithm which allows
for accurate calculation of excited states. We find excellent quantitative
agreement with the theoretical predictions and conclude that a pure Gaussian
model, without any orbifold construction, describes correctly the low-energy
physics of these critical phases. This combined analysis indicates that the
multicritical point at large single-ion anisotropy does not belong to the same
universality class as the Takhtajan-Babujian Hamiltonian as claimed in the
past. A link between string-order correlation functions and twisting vertex
operators, along the c=1 line that ends at this point, is also suggested.Comment: 9 pages, 3 figures, svjour format, submitted to Eur. Phys. J.
DMRG Simulation of the SU(3) AFM Heisenberg Model
We analyze the antiferromagnetic Heisenberg chain by means of
the Density Matrix Renormalization Group (DMRG). The results confirm that the
model is critical and the computation of its central charge and the scaling
dimensions of the first excited states show that the underlying low energy
conformal field theory is the Wess-Zumino-Novikov-Witten
model.Comment: corrections and improvements adde
Magnetic properties of commensurate Bose-Bose mixtures in one-dimensional optical lattices
We investigate magnetic properties of strongly interacting bosonic mixtures
confined in one dimensional geometries, focusing on recently realized Rb-K
gases with tunable interspecies interactions. By combining analytical
perturbation theory results with density-matrix-renormalization group
calculations, we provide quantitative estimates of the ground state phase
diagram as a function of the relevant microscopic quantities, identifying the
more favorable experimental regimes in order to access the various magnetic
phases. Finally, we qualitatively discuss the observability of such phases in
realistic setups when finite temperature effects have to be considered.Comment: 9 pages, 7 figures, to be published in EPJ ST special issue on "Novel
Quantum Phases and Mesoscopic Physics in Quantum Gases
Lattices and Their Continuum Limits
We address the problem of the continuum limit for a system of Hausdorff
lattices (namely lattices of isolated points) approximating a topological space
. The correct framework is that of projective systems. The projective limit
is a universal space from which can be recovered as a quotient. We dualize
the construction to approximate the algebra of continuous
functions on . In a companion paper we shall extend this analysis to systems
of noncommutative lattices (non Hausdorff lattices).Comment: 11 pages, 1 Figure included in the LaTeX Source New version, minor
modifications (typos corrected) and a correction in the list of author
Phase separation and pairing regimes in the one-dimensional asymmetric Hubbard model
We address some open questions regarding the phase diagram of the
one-dimensional Hubbard model with asymmetric hopping coefficients and balanced
species. In the attractive regime we present a numerical study of the passage
from on-site pairing dominant correlations at small asymmetries to
charge-density waves in the region with markedly different hopping
coefficients. In the repulsive regime we exploit two analytical treatments in
the strong- and weak-coupling regimes in order to locate the onset of phase
separation at small and large asymmetries respectively.Comment: 13 pages, RevTeX 4, 12 eps figures, some additional refs. with
respect to v1 and citation errors fixe
Variable Curvature Slab Molecular Dynamics as a Method to Determine Surface Stress
A thin plate or slab, prepared so that opposite faces have different surface
stresses, will bend as a result of the stress difference. We have developed a
classical molecular dynamics (MD) formulation where (similar in spirit to
constant-pressure MD) the curvature of the slab enters as an additional
dynamical degree of freedom. The equations of motion of the atoms have been
modified according to a variable metric, and an additional equation of motion
for the curvature is introduced. We demonstrate the method to Au surfaces, both
clean and covered with Pb adsorbates, using many-body glue potentials.
Applications to stepped surfaces, deconstruction and other surface phenomena
are under study.Comment: 16 pages, 8 figures, REVTeX, submitted to Physical Review
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