Category:DFT+U: Difference between revisions

The LDA and semilocal GGA functionals often fail to describe systems with localized (strongly correlated) [math]\displaystyle{ d }[/math] or [math]\displaystyle{ f }[/math] electrons (this manifests itself primarily in the form of unrealistic one-electron energies or too small magnetic moments in the case of systems with [math]\displaystyle{ d }[/math] electrons). In some cases this can be remedied by introducing on the [math]\displaystyle{ d }[/math] or [math]\displaystyle{ f }[/math] atom a strong intra-atomic interaction in a simplified (screened) Hartree-Fock like manner ([math]\displaystyle{ E_{\text{HF}}(\hat{n}) }[/math]), as an on-site replacement of the semilocal functional (double-counting term [math]\displaystyle{ E_{\text{dc}}(\hat{n}) }[/math]):

[math]\displaystyle{ E_{\text{xc}}^{\text{LDA/GGA}+U}(n,\hat{n}) = E_{\text{xc}}^{\text{LDA/GGA}}(n) + E_{\text{HF}}(\hat{n}) - E_{\text{dc}}(\hat{n}) }[/math]

where [math]\displaystyle{ \hat{n} }[/math] is the on-site occupancy matrix of the [math]\displaystyle{ d }[/math] or [math]\displaystyle{ f }[/math] electrons. This approach is known as the DFT+U method (traditionally called LSDA+U^[1] ).

The first VASP DFT+U calculations, including some additional technical details on the VASP implementation, can be found in Ref. ^[2] (the original implementation was done by Olivier Bengone ^[3] and Georg Kresse).

More detail about the formalism of the HF method and hybrids can be found here.

How to

DFT+U can be switched on with the LDAU tag in the INCAR file, while the LDAUTYPE tag determines the DFT+U flavor that is used.

References