Search results for "Monte Carlo method"
showing 10 items of 1234 documents
Monte Carlo study of cluster-diameter distribution: An observable to estimate correlation lengths
1997
We report numerical simulations of two-dimensional $q$-state Potts models with emphasis on a new quantity for the computation of spatial correlation lengths. This quantity is the cluster-diameter distribution function $G_{diam}(x)$, which measures the distribution of the diameter of stochastically defined cluster. Theoretically it is predicted to fall off exponentially for large diameter $x$, $G_{diam} \propto \exp(-x/\xi)$, where $\xi$ is the correlation length as usually defined through the large-distance behavior of two-point correlation functions. The results of our extensive Monte Carlo study in the disordered phase of the models with $q=10$, 15, and $20$ on large square lattices of si…
Quantum Monte Carlo study of insulating state in NaV2O5
2003
Abstract Quantum Monte Carlo (QMC) methods are being increasingly used as complements to Hartree–Fock (HF) methods for computing the electronic structure of molecules and materials. We investigate the nature of the insulating state driven by electronic correlations in the ladder compound NaV 2 O 5 ; considered as a quarter-filled system. We use an extended Hubbard model (EHM) to study the role of on-site and inter-site Coulomb interaction. It is found that the insulating state in the charge-disordered phase of this compound take origin from the transfer of spectral density and dynamical fluctuations. Our calculation allows us also, to understand the origin of the insulating states above T C…
Monte Carlo Study of Dense Monolayer and Bilayer Films on the (100) Plane of Face-Centered Cubic Crystals
1999
A Monte Carlo simulation method in the canonical and in the grand canonical ensembles is used to study the behavior and properties of dense monolayer and bilayer films formed on the (100) plane of model face-centered cubic crystals. Systems with different effects due to the periodicity of the gas−solid potential are considered, and the mechanism of melting in the first and the second adsorbed layer is discussed. It is demonstrated that the film structure is very sensitive to the gas−solid potential corrugation, as well as to the temperature and the surface coverage. In particular, it is shown that monolayer films formed on weakly corrugated surfaces exhibit the incommensurate (dense) phase …
Lattice gas models for multilayer adsorption: variation of phase diagrams with the strength of the substrate potential
1990
Abstract The simple cubic lattice gas model with nearest-neighbor attractive interaction is considered for the case where the potential V ( z ), that an adatom at a distance z from the surface experiences due to the substrate, is V ( z ) = − A / z 3 . Exact ground state phase diagrams are obtained for different A , while the behavior at nonzero temperatures is studied both by Monte Carlo simulations and the molecular field approximation. We show that the detailed sequence of the layering transitions in the first few layers depends very strongly on the strength of the substrate potential: for strong potentials individual first-order layering transitions in layers 1, 2, 3, …, while for interm…
Flexible Estimation of Heteroskedastic Stochastic Frontier Models via Two-step Iterative Nonlinear Least Squares
2019
Despite its importance, the monotonicity condition is typically overlooked in stochastic frontier analysis. This article illustrates a straightforward and useful method for the estimation of semiparametric stochastic frontier models imposing such constraint and incorporating exogenous inefficiency effects exploiting the scaling property. An iterative estimation algorithm based on nonlinear least squares is developed and the behavior of the proposed procedure is investigated through a set of Monte Carlo experiments comparing its finite sample properties with those of available alternatives. The simulation results highlight very good performance of the new algorithm which outperforms the comp…
Efficient simulation of the random-cluster model
2013
The simulation of spin models close to critical points of continuous phase transitions is heavily impeded by the occurrence of critical slowing down. A number of cluster algorithms, usually based on the Fortuin-Kasteleyn representation of the Potts model, and suitable generalizations for continuous-spin models have been used to increase simulation efficiency. The first algorithm making use of this representation, suggested by Sweeny in 1983, has not found widespread adoption due to problems in its implementation. However, it has been recently shown that it is indeed more efficient in reducing critical slowing down than the more well-known algorithm due to Swendsen and Wang. Here, we present…
Can hydrophobic interactions be correctly reproduced by the continuum models?
1996
The ability of the continuum models to describe hydrophobic interactions is investigated. In this work we have studied the interactions between two methane molecules in aqueous solution by means of a continuum model. The resulting potential of mean force is in good agreement with those obtained using Monte Carlo and molecular dynamics techniques. The three energy contributions appearing in the continuum energy partition (electrostatic, dispersion−repulsion, and cavitation) have been analyzed. The cavitation free energy plays the most important role of the three, determining the existence of an energy barrier between the contact minimum and the separated methane monomers. This barrier, which…
Reconstruction of random media using Monte Carlo methods.
1998
A simulated annealing algorithm is applied to the reconstruction of two-dimensional porous media with prescribed correlation functions. The experimental correlation function of an isotropic sample of Fontainebleau sandstone and a synthetic correlation function with damped oscillations are used in the reconstructions. To reduce the numerical effort we follow a proposal suggesting the evaluation of the correlation functions only along certain directions. The results show that this simplification yields significantly different microstructures as compared to a full evaluation of the correlation function. In particular, we find that the simplified reconstruction method introduces an artificial a…
Monte Carlo estimation of transverse and longitudinal correlation functions in the model
2010
Abstract Monte Carlo simulations of the three-dimensional O ( 4 ) model in the ordered phase are performed to study the Goldstone mode effects. Our data show a distinct scaling region, where the Fourier-transformed transverse correlation function behaves as ∝ k − λ ⊥ with λ ⊥ 2 ( λ ≃ 1.95 ), in disagreement with the standard theoretical prediction λ ⊥ = 2 .
The Tax Returns of Public Spending on Universities: An Estimate with Monte Carlo Simulations
2015
Pastor J. M. and Peraita C. The tax returns of public spending on universities: an estimate with Monte Carlo simulations, Regional Studies. This paper proposes a methodology based on counterfactual scenarios and the existence of uncertainty to estimate the tax returns of public spending of regional governments on their public universities. The introduction of differences in the time spent by the students at university and the proportion of the total public expenditure implies making assumptions about uncertainty. The paper applies Monte Carlo simulations incorporating stochastic elements to estimate the tax returns of public spending in the University of the Basque Country (Spain). The resu…