SIESTA is an original method and its computer program implementation, to perform efficient electronic structure calculations and ab initiomolecular dynamics simulations of molecules and solids. SIESTA's efficiency stems from the use of strictly localized basis sets and from the implementation of linear-scaling algorithms which can be applied to suitable systems. A very important feature of the code is that its accuracy and cost 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 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 GPLopen-source license. Source packages and access to the development versions can be obtained from the .
It uses norm-conserving pseudopotentials in their fully nonlocal form.
It uses atomic orbitals 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 for calculating the Hamiltonian and overlap matrices in O 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, making the computer time and memory scale linearly with the number of atoms. Simulations with several hundred atoms are feasible with modest workstations.
It is written in Fortran 95 and memory is allocated dynamically.
It may be compiled for serial or parallel execution.
The use of 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 computing systems with a thousand of atoms. At the same time, the use of more complete and accurate bases allows to achieve accuracies comparable to those of standard plane waves calculations, still at an advantageous computational cost.
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 calculations
Efficient implementation of Van der Waals functional
A number of post-processing tools for SIESTA have been developed. These programs can be helpful to process SIESTA output, or to supplement the functionality of the program.
Applications
Since its implementation, SIESTA has become quite popular, being increasingly used by researchers in geosciences, biology, and engineering and has been applied to a large variety of systems including surfaces, adsorbates, nanotubes, nanoclusters, biological molecules, amorphous semiconductors, ferroelectric films, low-dimensional metals, etc.
