VASP is a package for performing ab-initio quantum-mechanical molecular dynamics (MD) using pseudopotentials and a plane wave basis set.
VASP is a complex package for performing ab-initio quantum-mechanical molecular dynamics (MD) simulations using pseudopotentials or the projector-augmented wave method and a plane wave basis set. The approach implemented in VASP is based on the (finite-temperature) local-density approximation with the free energy as variational quantity and an exact evaluation of the instantaneous electronic ground state at each MD time step. VASP uses efficient matrix diagonalisation schemes and an efficient Pulay/Broyden charge density mixing. These techniques avoid all problems possibly occurring in the original Car-Parrinello method, which is based on the simultaneous integration of electronic and ionic equations of motion. The interaction between ions and electrons is described by ultra-soft Vanderbilt pseudopotentials (US-PP) or by the projector-augmented wave (PAW) method. US-PP (and the PAW method) allow for a considerable reduction of the number of plane-waves per atom for transition metals and first row elements. Forces and the full stress tensor can be calculated with VASP and used to relax atoms into their instantaneous ground-state.For more information visit: http://cms.mpi.univie.ac.at/vasp/. A link to the local tutorial is available here.
Here is a short summary of some highlights of the VASP code:
- VASP uses the PAW method or ultra-soft pseudopotentials. Therefore the size of the basis-set can be kept very small even for transition metals and first row elements like C and O. Generally not more than 100 plane waves (PW) per atom are required to describe bulk materials, in most cases even 50 PW per atom will be sufficient for a reliable description.
- In any plane wave program, the execution time scales like for some parts of the code, where is the number of valence electrons in the system. In the VASP, the pre-factors for the cubic parts are almost negligible leading to an efficient scaling with respect to system size. This is possible by evaluating the non local contributions to the potentials in real space and by keeping the number of orthogonalisations small. For systems with roughly 2000 electronic bands, the part becomes comparable to other parts. Hence we expect VASP to be useful for systems with up to 4000 valence electrons.
- VASP uses a rather ``traditional'' and ``old fashioned'' self-consistency cycle to calculate the electronic ground-state. The combination of this scheme with efficient numerical methods leads to an efficient, robust and fast scheme for evaluating the self-consistent solution of the Kohn-Sham functional. The implemented iterative matrix diagonalisation schemes (RMM-DISS, and blocked Davidson) are probably among the fastest schemes currently available.
- VASP includes a full featured symmetry code which determines the symmetry of arbitrary configurations automatically.
- The symmetry code is also used to set up the Monkhorst Pack special points allowing an efficient calculation of bulk materials, symmetric clusters. The integration of the band-structure energy over the Brillouin zone is performed with smearing or tetrahedron methods. For the tetrahedron method, Blöchl's corrections, which remove the quadratic error of the linear tetrahedron method, can be used resulting in a fast convergence speed with respect to the number of special points.
- VASP runs equally well on super-scalar processors, vector computers and parallel computers.