Requests for technical support from the VASP group should be posted in the VASP-forum.
The LDA and semilocal GGA functionals often fail to describe systems with localized (strongly correlated) or electrons (this manifests itself primarily in the form of unrealistic one-electron energies or too small magnetic moments in the case of systems with electrons). In some cases this can be remedied by introducing on the or atom a strong intra-atomic interaction in a simplified (screened) Hartree-Fock like manner (), as an on-site replacement of the semilocal functional (double-counting term ):
where is the on-site occupancy matrix of the or electrons. This approach is known as the DFT+U method (traditionally called LSDA+U ).
The first VASP DFT+U calculations, including some additional technical details on the VASP implementation, can be found in Ref.  (the original implementation was done by Olivier Bengone  and Georg Kresse).
More detail about the formalism of the DFT+U method can be found here.