SIESTA (computer program): Difference between revisions

Revision as of 03:29, 24 December 2022

Revision as of 08:49, 5 March 2023

Line 47:

}}

'''SIESTA''' ('''Spanish Initiative for Electronic Simulations with Thousands of Atoms''') is an original method and its computer program implementation, to efficiently perform [[electronic structure]] calculations and [[ab initio]] [[molecular dynamics]] simulations of [[molecules]] and solids. SIESTA uses of strictly localized basis sets and from the implementation of linear-scaling algorithms. Accuracy and speed can be tuned in a wide range, from quick exploratory calculations to highly accurate simulations matching the quality of other approaches, such as plane-wave and all-electron methods.

SIESTA's [[backronym]] is the Spanish Initiative for Electronic Simulations with Thousands of Atoms.

Since 13 May 2016, with the 4.0 version announcement, SIESTA is released under the terms of the [[GPL]] open-source license. Source packages and access to the development versions can be obtained from the [[DevOps]] platform on [[GitLab]].<ref>{{cite web|url=https://gitlab.com/siesta-project/siesta/|title=SIESTA development platform on GitLab.}}</ref> The latest version Siesta-4.1.5 was released on 4 February 2021.

Line 57:

* It uses the standard Kohn-Sham self-consistent [[Density functional theory|density functional]] method in the [[Local-density approximation|local density]] (LDA-LSD) and generalized gradient (GGA) approximations, as well as in a non-local function that includes [[van der Waals interactions]] (VDW-DF).

* It uses norm-conserving [[pseudopotential]]s in their fully non-local (Kleinman-Bylander) form.

* It uses [[atomic orbital]]s as a basis set, allowing unlimited multiple-zeta and angular momenta, polarization and off-site orbitals. The radial shape of every orbital is numerical, and any shape can be used and provided by the user, with the only condition that it has to be of finite support, i.e., it has to be strictly zero beyond a user-provided distance from the corresponding nucleus. Finite-support basis sets are the key forto calculating the Hamiltonian and overlap matrices in O(N) operations.

* Projects the electron wavefunctions and density onto a real-space grid in order to calculate the Hartree and exchange-correlation potentials and their matrix elements.

* Besides the standard Rayleigh-Ritz eigenstate method, it allows the use of localized linear combinations of the occupied orbitals (valence-bond or Wannier-like functions), making the computer time and memory scale linearly with the number of atoms. Simulations with several hundred atoms are feasible with modest workstations.

Line 88:

# It can tackle computationally demanding systems (systems currently out of the reach of plane-wave codes).{{Citation needed|date=November 2021}}

# Efficient parallelization.

The use of a linear combination of numerical atomic orbitals makes SIESTA a flexible and efficient DFT code. SIESTA is able to produce very fast calculations with small basis sets, allowing the computation of systems with thousands of atoms. Alternatively, the use of more complete and accurate bases achieves accuracies comparable to those of standard plane waves calculations, with competitive performance.

== Implemented Solutions ==

SIESTA is in continuous development since it was implemented in 1996. The main solutions implemented in the current version are:

* Collinear and non-collinear spin polarized-polarised calculations

* Efficient implementation of Van der Waals functional

* [[Wannier function]] implementation