6,142 research outputs found
Ab-Initio Molecular Dynamics
Computer simulation methods, such as Monte Carlo or Molecular Dynamics, are
very powerful computational techniques that provide detailed and essentially
exact information on classical many-body problems. With the advent of ab-initio
molecular dynamics, where the forces are computed on-the-fly by accurate
electronic structure calculations, the scope of either method has been greatly
extended. This new approach, which unifies Newton's and Schr\"odinger's
equations, allows for complex simulations without relying on any adjustable
parameter. This review is intended to outline the basic principles as well as a
survey of the field. Beginning with the derivation of Born-Oppenheimer
molecular dynamics, the Car-Parrinello method and the recently devised
efficient and accurate Car-Parrinello-like approach to Born-Oppenheimer
molecular dynamics, which unifies best of both schemes are discussed. The
predictive power of this novel second-generation Car-Parrinello approach is
demonstrated by a series of applications ranging from liquid metals, to
semiconductors and water. This development allows for ab-initio molecular
dynamics simulations on much larger length and time scales than previously
thought feasible.Comment: 13 pages, 3 figure
A Hybrid Decomposition Parallel Implementation of the Car-Parrinello Method
We have developed a flexible hybrid decomposition parallel implementation of
the first-principles molecular dynamics algorithm of Car and Parrinello. The
code allows the problem to be decomposed either spatially, over the electronic
orbitals, or any combination of the two. Performance statistics for 32, 64, 128
and 512 Si atom runs on the Touchstone Delta and Intel Paragon parallel
supercomputers and comparison with the performance of an optimized code running
the smaller systems on the Cray Y-MP and C90 are presented.Comment: Accepted by Computer Physics Communications, latex, 34 pages without
figures, 15 figures available in PostScript form via WWW at
http://www-theory.chem.washington.edu/~wiggs/hyb_figures.htm
Coupled Electron Ion Monte Carlo Calculations of Dense Metallic Hydrogen
We present a new Monte Carlo method which couples Path Integral for finite
temperature protons with Quantum Monte Carlo for ground state electrons, and we
apply it to metallic hydrogen for pressures beyond molecular dissociation. We
report data for the equation of state for temperatures across the melting of
the proton crystal. Our data exhibit more structure and higher melting
temperatures of the proton crystal than Car-Parrinello Molecular Dynamics
results. This method fills the gap between high temperature electron-proton
Path Integral and ground state Diffusion Monte Carlo methods
Coulomb Interactions via Local Dynamics: A Molecular--Dynamics Algorithm
We derive and describe in detail a recently proposed method for obtaining
Coulomb interactions as the potential of mean force between charges which are
dynamically coupled to a local electromagnetic field. We focus on the Molecular
Dynamics version of the method and show that it is intimately related to the
Car--Parrinello approach, while being equivalent to solving Maxwell's equations
with freely adjustable speed of light. Unphysical self--energies arise as a
result of the lattice interpolation of charges, and are corrected by a
subtraction scheme based on the exact lattice Green's function. The method can
be straightforwardly parallelized using standard domain decomposition. Some
preliminary benchmark results are presented.Comment: 8 figure
Grand-Canonical Quantized Liquid Density-Functional Theory in a Car-Parrinello Implementation
Quantized Liquid Density-Functional Theory [Phys. Rev. E 2009, 80, 031603], a
method developed to assess the adsorption of gas molecules in porous
nanomaterials, is reformulated within the grand canonical ensemble. With the
grand potential it is possible to compare directly external and internal
thermodynamic quantities. In our new implementation, the grand potential is
minimized utilizing the Car-Parrinello approach and gives, in particular for
low temperature simulations, a significant computational advantage over the
original canonical approaches. The method is validated against original QLDFT,
and applied to model potentials and graphite slit pores.Comment: 19 pages, 5 figure
Polymers near Metal Surfaces: Selective Adsorption and Global Conformations
We study the properties of a polycarbonate melt near a nickel surface as a
model system for the interaction of polymers with metal surfaces by employing a
multiscale modeling approach. For bulk properties a suitably coarse grained
bead spring model is simulated by molecular dynamics (MD) methods with model
parameters directly derived from quantum chemical calculations. The surface
interactions are parameterized and incorporated by extensive quantum mechanical
density functional calculations using the Car-Parrinello method. We find strong
chemisorption of chain ends, resulting in significant modifications of the melt
composition when compared to an inert wall.Comment: 8 pages, 3 figures (2 color), 1 tabl
- …