The Vienna Ab initio Simulation Package, better known as VASP, is a package written primarily in Fortran for performing ab initio quantum mechanical calculations using either Vanderbilt pseudopotentials, or the projector augmented wave method, and a plane wave basis set. The basic methodology is density functional theory (DFT), but the code also allows use of post-DFT corrections such as hybrid functionals mixing DFT and Hartree–Fock exchange (e.g. HSE, PBE0 or B3LYP), many-body perturbation theory (the GW method) and dynamical electronic correlations within the random phase approximation (RPA) and MP2.