43 research outputs found
Real-space density functional theory and time dependent density functional theory using finite/infinite element methods
We present a numerical approach using the finite element method to discretize the equations that allow getting a first-principles description of multi-electronic systems within DFT and TD-DFT formalisms. A strictly local polynomial function basis set is used in order to represent the entire real-space domain. Infinite elements are introduced to model the infinite external boundaries in the case of Hartree's equation. The diagonal mass matrix is obtained using a close integration rule, reducing the generalized eigenvalue problem to a standard one. This framework of electronic structure calculation is embedded in a high performance computing environment with a very good parallel behavior.Fil: Soba, Alejandro. Barcelona Supercomputing Center - Centro Nacional de Supercomputacion; España. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Bea, Edgar Alejandro. Barcelona Supercomputing Center - Centro Nacional de Supercomputacion; España. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Houzeaux, Guillaume. Barcelona Supercomputing Center - Centro Nacional de Supercomputacion; EspañaFil: Calmet, Hadrien. Barcelona Supercomputing Center - Centro Nacional de Supercomputacion; EspañaFil: Cela, JosĂ© MarĂa. Barcelona Supercomputing Center - Centro Nacional de Supercomputacion; Españ
Three real-space discretization techniques in electronic structure calculations
A characteristic feature of the state-of-the-art of real-space methods in
electronic structure calculations is the diversity of the techniques used in
the discretization of the relevant partial differential equations. In this
context, the main approaches include finite-difference methods, various types
of finite-elements and wavelets. This paper reports on the results of several
code development projects that approach problems related to the electronic
structure using these three different discretization methods. We review the
ideas behind these methods, give examples of their applications, and discuss
their similarities and differences.Comment: 39 pages, 10 figures, accepted to a special issue of "physica status
solidi (b) - basic solid state physics" devoted to the CECAM workshop "State
of the art developments and perspectives of real-space electronic structure
techniques in condensed matter and molecular physics". v2: Minor stylistic
and typographical changes, partly inspired by referee comment
Gradient type optimization methods for electronic structure calculations
The density functional theory (DFT) in electronic structure calculations can
be formulated as either a nonlinear eigenvalue or direct minimization problem.
The most widely used approach for solving the former is the so-called
self-consistent field (SCF) iteration. A common observation is that the
convergence of SCF is not clear theoretically while approaches with convergence
guarantee for solving the latter are often not competitive to SCF numerically.
In this paper, we study gradient type methods for solving the direct
minimization problem by constructing new iterations along the gradient on the
Stiefel manifold. Global convergence (i.e., convergence to a stationary point
from any initial solution) as well as local convergence rate follows from the
standard theory for optimization on manifold directly. A major computational
advantage is that the computation of linear eigenvalue problems is no longer
needed. The main costs of our approaches arise from the assembling of the total
energy functional and its gradient and the projection onto the manifold. These
tasks are cheaper than eigenvalue computation and they are often more suitable
for parallelization as long as the evaluation of the total energy functional
and its gradient is efficient. Numerical results show that they can outperform
SCF consistently on many practically large systems.Comment: 24 pages, 11 figures, 59 references, and 1 acknowledgement
Towards chemical accuracy using a multi-mesh adaptive finite element method in all-electron density functional theory
Chemical accuracy serves as an important metric for assessing the
effectiveness of the numerical method in Kohn--Sham density functional theory.
It is found that to achieve chemical accuracy, not only the Kohn--Sham
wavefunctions but also the Hartree potential, should be approximated
accurately. Under the adaptive finite element framework, this can be
implemented by constructing the \emph{a posteriori} error indicator based on
approximations of the aforementioned two quantities. However, this way results
in a large amount of computational cost. To reduce the computational cost, we
propose a novel multi-mesh adaptive method, in which the Kohn--Sham equation
and the Poisson equation are solved in two different meshes on the same
computational domain, respectively. With the proposed method, chemical accuracy
can be achieved with less computational consumption compared with the adaptive
method on a single mesh, as demonstrated in a number of numerical experiments.Comment: 19pages, 17 figure
Adaptive Finite Element Approximations for Kohn-Sham Models
The Kohn-Sham equation is a powerful, widely used approach for computation of
ground state electronic energies and densities in chemistry, materials science,
biology, and nanosciences. In this paper, we study the adaptive finite element
approximations for the Kohn-Sham model. Based on the residual type a posteriori
error estimators proposed in this paper, we introduce an adaptive finite
element algorithm with a quite general marking strategy and prove the
convergence of the adaptive finite element approximations. Using D{\" o}rfler's
marking strategy, we then get the convergence rate and quasi-optimal
complexity. We also carry out several typical numerical experiments that not
only support our theory,but also show the robustness and efficiency of the
adaptive finite element computations in electronic structure calculations.Comment: 38pages, 7figure