NMAXFOCKAE
NMAXFOCKAE = 1|2
Default: NMAXFOCKAE = 1
Description: NMAXFOCKAE determines the maximum order of expansion for augmentation charges used in shape restoration for the PAW method.
NMAXFOCKAE controls how accurately this augmentation is performed by specifying the maximum expansion order. It controls the plane-wave cutoff up to which accurate charge densities are restored on the plane-wave grid. Shape restoration is only accurate up to a certain plane-wave cutoff, typically about 150 eV for NMAXFOCKAE = 1, and 400 eV for NMAXFOCKAE = 2.
| Important: Shape restoration is more fully documented in the LMAXFOCKAE page. Additionally, see Ref. [1] and [2]. |
| Mind: This flag generally only applies to the Fock-exchange and many-body perturbation theory (MBPT) methods (GW, RPA, MP2, etc.). |
Recommendations
NMAXFOCKAE = 1is sufficient in most cases and provides a good balance between accuracy and computational cost. It predicts very accurate energy differences and quite accurate quasiparticle energies.NMAXFOCKAE = 2should be used with great caution. Specifically, noise and egg-box effects for coarse FFT grids are introduced as NMAXFOCKAE is increased. Use this flag only after extensive tests and verification that the increased accuracy is needed for your application. It yields very accurate results for post-DFT methods (MP2, RPA, GW) even for difficult 3d elements.- For GW calculations, increasing from
NMAXFOCKAE = 1toNMAXFOCKAE = 2might change quasiparticle energies by 100-200 meV for 3d and late 4d and 5d elements. - For RPA and MP2 total energy calculations, differences between
NMAXFOCKAE = 1andNMAXFOCKAE = 2are usually small for total energy differences.
- For GW calculations, increasing from
Mind: Since absolute correlation energies might change, it is vital to use the same setting for NMAXFOCKAE and LMAXFOCKAE, if energy differences are calculated. Please check whether the VASP default setting for LMAXFOCKAE suffices (OUTCAR file). Use this setting only with care, as it can result in very noisy data for coarse FFT grids.
Related tags and articles
NMAXFOCKAE, LMAXFOCK, QMAXFOCKAE, LFOCKAEDFT, LFOCKSTD