The POTCAR file contains information on the energy of the atom in the reference configuration (i.e. the configuration for which the PP was generated). Total energies calculated by vasp are with respect to this configuration. The reference calculation, however, did not allow for spin-polarisation or broken symmetry solutions, which usually lower the energy for gradient corrected of hybrid functionals. To include these effects properly, it is required to calculate the lowest energy magnetic groundstate using VASP.
Unfortunately convergence to the symmetry broken spin polarized groundstate can be relatively slow in VASP. The following INCAR file worked reasonably well for most elements:
ISYM = 0 # no symmetry ISPIN = 2 # allow for spin polarisation VOSKOWN = 1 # this is important, in particular for GGA # but not required for PBE potentials ISMEAR = 0 # Gaussian smearing, otherwise negative occupancies might come up SIGMA = 0.002 # tiny smearing width to safely break symmetry AMIX = 0.2 # mixing set manually BMIX = 0.0001 NELM = 100 # often many steps are required ICHARG = 1Execute VASP twice to three times, consecutively with this input file until energies are converged. Furthermore, we recommend to use large slightly non-cubic cells, i.e. 12 Å13 Å14 Å. In some cases, we also found it advantageously to use direct energy minimization instead of charge-density mixing
ALGO = D ; LSUBROT = .FALSE. ; NELM = 500 ; TIME = 0.2or
ALGO = A ; LSUBROT = .FALSE. ; NELM = 500 ; TIME = 0.2Always check for convergence, and whether all occupancies are 0 or 1.