502 research outputs found
Electronic structure calculations and molecular dynamics simulations with linear system-size scaling
We present a method for total energy minimizations and molecular dynamics
simulations based either on tight-binding or on Kohn-Sham hamiltonians. The
method leads to an algorithm whose computational cost scales linearly with the
system size. The key features of our approach are
(i) an orbital formulation with single particle wavefunctions constrained to
be localized in given regions of space, and (ii) an energy functional which
does not require either explicit orthogonalization of the electronic orbitals,
or inversion of an overlap matrix.
The foundations and accuracy of the approach and the performances of the
algorithm are discussed, and illustrated with several numerical examples
including Kohn-Sham hamiltonians. In particular we present calculations with
tight-binding hamiltonians for diamond, graphite, a carbon linear chain and
liquid carbon at low pressure. Even for a complex case such as liquid carbon --
a disordered metallic system with differently coordinated atoms -- the
agreement between standard diagonalization schemes and our approach is very
good. Our results establish the accuracy and reliability of the method for a
wide class of systems and show that tight binding molecular dynamics
simulations with a few thousand atoms are feasible on small workstations
Daubechies wavelets as a basis set for density functional pseudopotential calculations
Daubechies wavelets are a powerful systematic basis set for electronic
structure calculations because they are orthogonal and localized both in real
and Fourier space. We describe in detail how this basis set can be used to
obtain a highly efficient and accurate method for density functional electronic
structure calculations. An implementation of this method is available in the
ABINIT free software package. This code shows high systematic convergence
properties, very good performances and an excellent efficiency for parallel
calculations.Comment: 15 pages, 11 figure
Application of A Distributed Nucleus Approximation In Grid Based Minimization of the Kohn-Sham Energy Functional
In the distributed nucleus approximation we represent the singular nucleus as
smeared over a smallportion of a Cartesian grid. Delocalizing the nucleus
allows us to solve the Poisson equation for theoverall electrostatic potential
using a linear scaling multigrid algorithm.This work is done in the context of
minimizing the Kohn-Sham energy functionaldirectly in real space with a
multiscale approach. The efficacy of the approximation is illustrated
bylocating the ground state density of simple one electron atoms and
moleculesand more complicated multiorbital systems.Comment: Submitted to JCP (July 1, 1995 Issue), latex, 27pages, 2figure
Object-oriented construction of a multigrid electronic-structure code with Fortran 90
We describe the object-oriented implementation of a higher-order
finite-difference density-functional code in Fortran 90. Object-oriented models
of grid and related objects are constructed and employed for the implementation
of an efficient one-way multigrid method we have recently proposed for the
density-functional electronic-structure calculations. Detailed analysis of
performance and strategy of the one-way multigrid scheme will be presented.Comment: 24 pages, 6 figures, to appear in Comput. Phys. Com
Large Scale Electronic Structure Calculations with Multigrid Acceleration
We have developed a set of techniques for performing large scale ab initio
calculations using multigrid accelerations and a real-space grid as a basis.
The multigrid methods permit efficient calculations on ill-conditioned systems
with long length scales or high energy cutoffs. The technique has been applied
to systems containing up to 100 atoms, including a highly elongated diamond
cell, an isolated C molecule, and a 32-atom cell of GaN with the Ga
d-states in valence. The method is well suited for implementation on both
vector and massively parallel architectures.Comment: 4 pages, 1 postscript figur
- …