Quantum Monte Carlo simulation

Contemporary scientific studies often rely on the understanding of complex quantum systems via computer simulation. This paper initiates the statistical study of quantum simulation and proposes a Monte Carlo method for estimating analytically intractable quantities. We derive the bias and variance for the proposed Monte Carlo quantum simulation estimator and establish the asymptotic theory for the estimator. The theory is used to design a computational scheme for minimizing the mean square error of the estimator.Comment: Published in at http://dx.doi.org/10.1214/10-AOAS406 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Effect of a heterogeneous distribution of particles on the formation of banded grain structure in wrought Alloy 718

Alloy 718 is known to be sensitive to interdendritic segregation formed during ingot solidification. The occurrence of banded grain structures under heat treating conditions close to 1000 ° C related to interdendritic segregation is often reported. In order to have a better understanding of this microstructural evolution, an extensive experimental program has been carried out. Consequently, a model taking into account the selective dissolution of δ-phase (Ni3Nb) is proposed. A grain growth simulation by Monte-Carlo method is then used to illustrate the grain structure evolution in a banded particle distribution. By comparing experimental data and computer simulation, the relationship between the Monte-Carlo step and the real time is assessed and the range of parameters when heterogeneous microstructures appear is specified

Quantum Monte Carlo Simulation of the High-Pressure Molecular-Atomic Crossover in Fluid Hydrogen

A first-order liquid-liquid phase transition in high-pressure hydrogen between molecular and atomic fluid phases has been predicted in computer simulations using ab initio molecular dynamics approaches. However, experiments indicate that molecular dissociation may occur through a continuous crossover rather than a first-order transition. Here we study the nature of molecular dissociation in fluid hydrogen using an alternative simulation technique in which electronic correlation is computed within quantum Monte Carlo, the so-called Coupled Electron Ion Monte Carlo (CEIMC) method. We find no evidence for a first-order liquid-liquid phase transition.Comment: 4 pages, 5 figures; content changed; accepted for publication in Phys. Rev. Let

Monte Carlo Simulation of Comptonization in Inhomogeneous Media

Comptonization is the process in which photon spectrum changes due to multiple Compton scatterings in the electronic plasma. It plays an important role in the spectral formation of astrophysical X-ray and gamma-ray sources. There are several intrinsic limitations for the analytical method in dealing with the Comptonization problem and Monte Carlo simulation is one of the few alternatives. We describe an efficient Monte Carlo method that can solve the Comptonization problem in a fully relativistic way. We expanded the method so that it is capable of simulating Comptonization in the media where electron density and temperature varies discontinuously from one region to the other and in the isothermal media where density varies continuously along photon paths. The algorithms are presented in detail to facilitate computer code implementation. We also present a few examples of its application to the astrophysical research.Comment: 12 pages, 4 figures, Postscript file, in press ("Computers in Physics", Vol. 11, No. 6

On a simple and accurate quantum correction for Monte Carlo simulation

We investigate a quantum-correction method for Monte Carlo device simulation. The method consists of reproducing quantum mechanical density-gradient simulation by classical drift-diffusion simulation with modified effective oxide thickness and work function and using these modifications subsequently in Monte Carlo simulation. This approach is found to be highly accurate and can be used fully automatically in a technology computer-aided design (TCAD) workbench project. As an example, the methodology is applied to the Monte Carlo simulation of the on-current scaling in p- and n-type MOSFETs corresponding to a 65 nm node technology. In particular, it turns out that considering only the total threshold voltage shift still involves a significant difference to a Monte Carlo simulation based on the combined correction of oxide thickness and work function. Ultimately, this quantum correction permits to consider surface scattering as a combination of specular and diffusive scattering where the conservation of energy and parallel wave vector in the specular part takes stress-induced band structure modifications and hence the corresponding surface mobility changes on a physical basis into accoun

ZPC 1.0.1: a parton cascade for ultrarelativistic heavy ion collisions

A Monte Carlo program solving Boltzmann equation for partons via cascade method is presented. At presented, only gluon-gluon elastic scattering is included. The scattering cross section is regulated by a medium generated screening mass. Three different geometric modes (3 dimension expansion, 1-d expansion, and scattering inside a box) are provided for theoretical study of the parton transport and the applicability of the cascade method. Space cell division is available to save the number of computer operations. This improves the speed of the calculation by a large factor and makes the code best optimized for simulation of parton cascade in ultrarelativistic heavy ion collisions.Comment: LaTex, 25 pages, 3 figure