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OS: Linux, ...

License: free for academic users, Registration

Methods: DFT

SIESTA (Spanish Initiative for Electronic Simulations with Thousands of Atoms) is both a method and its computer program implementation, to perform electronic structure calculations and ab initio molecular dynamics simulations of molecules and solids. Its main characteristics are:

It uses the standard Kohn-Sham self-consistent density functional method in the local density (LDA-LSD) or generalized gradient (GGA) approximations.
It uses norm-conserving pseudopotentials in their fully nonlocal (Kleinman-Bylander) 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 $O(N)$ 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.
It is written in Fortran 95 and memory is allocated dynamically.
It may be compiled for serial or parallel execution (under MPI).

It routinely provides:

Total and partial energies.
Atomic forces.
Stress tensor.
Electric dipole moment.
Atomic, orbital and bond populations (Mulliken).
Electron density.

And also (though not all options are compatible):

Geometry relaxation, fixed or variable cell.
Constant-temperature molecular dynamics (Nose thermostat).
Variable cell dynamics (Parrinello-Rahman).
Spin polarized calculations (collinear or not).
k-sampling of the Brillouin zone.
Local and orbital-projected density of states.
COOP and COHP curves for chemical bonding analysis.
Dielectric polarization.
Vibrations (phonons).
Band structure.
Ballistic electron transport (through TRANSIESTA)