`PREC`= `Low | Medium | High | Normal | Accurate | Single`

Default: | ||

PREC= |
Medium | for VASP.4.X |

= | Normal | for VASP.5.X |

The settings `Normal` and `Accurate` are only available in VASP.4.5 and
newer versions. The setting `Single` is only available in VASP.5.1.

Changing the `PREC` parameter influences the default for four sets of parameters
(`ENCUT`; `NGX`, `NGY`, `NGZ`; `NGXF`, `NGYF`, `NGZF` and `ROPT`),
and it is also possible to obtain the same characteristics by changing
the corresponding parameters in the INCAR file (VASP.4.X) directly.

- The
`PREC`-flag determines the energy cutoff`ENCUT`, if (and only if) no value is given for`ENCUT`in the INCAR file. For`PREC=Low`,`ENCUT`will be set to the maximal`ENMIN`value found in the POTCAR files. For`PREC=Medium`and`PREC=Accurate`,`ENCUT`will be set to maximal`ENMAX`value found on the POTCAR file (see 5.4). Finally for`PREC=High`,`ENCUT`is set to the maximal`ENMAX`value in the POTCAR file plus 30%.`PREC=High`guarantees that the*absolute*energies are converged to a few meV, and it ensures that the stress tensor is converged within a few kBar. In general, an increased energy cutoff is only required for accurate evaluation of quantities related to the stress tensor (e.g. elastic properties).The following table summarizes how

`PREC`determines other flags in the INCAR file:`PREC``ENCUT``NG`x`NG`x`F``ROPT``Normal`max( `ENMAX`)3/2 2 `NG`x-5E-4 `Single`max( `ENMAX`)3/2 `NG`x-5E-4 `Accurate`max( `ENMAX`)2 2 `NG`x-2.5E-4 `Low`max( `ENMIN`)3/2 3 -1E-2 `Med`max( `ENMAX`)3/2 4 -2E-3 `High`max( `ENMAX`)*1.32 16/3 -4E-4 `ENMAX/`) corresponds to the maximum`ENMIN``ENMAX/`found in POTCAR`ENMIN`

`ENAUG`defaults to the maximum`EAUG`found in POTCAR - FFT-grids (
`NGX`,`NGY`,`NGZ`and`NGXF`,`NGYF`,`NGZF`):For

`PREC=High`and`PREC=Accurate`, wrap around errors are avoided (see section 7.2, all -vectors that are twice as large as the vectors included in the basis set are taken into account in the FFT's). For`PREC=Low`,`PREC=Medium`or`PREC=Normal`, the FFT grids are reduced, and 3/4 of the required values are used. Usually`PREC=Medium`and`PREC=Normal`, are sufficiently accurate with errors less than 1 meV/atom.In addition, the

`PREC`tag determines the spacing for the grids representing the augmentation charges, charge densities and potentials (NGFX, NGFY, NGFZ). For`PREC=Accurate`and`PREC=Normal`, the support grid contains twice as many points in each direction as the grids for the orbitals (`NGXF= 2 NGX, NGYF= 2 NGY, NGZF= 2 NGZ`).`PREC=Single`is identical to`PREC=Normal`, execpt that the double grid technique is not applied. This is convenient of you need to cut down on storage demands, or want to reduce the size of the CHG and CHGCAR file (for scanning tunneling microscopy simulation, it is recommended to use`PREC=Single`). In all other cases, they are determined by some rather heuristic formula from`ENAUG`(see Sec. 6.10). - If real space projectors are used,
`ROPT`(which controlls the number of grid points within the integration sphere around each ion, see Sec. 6.39) is set tofor

`LREAL=O`the defaults are:`PREC= Low`700 points in the real space sphere ( `ROPT`= 0.67)`PREC= Med`1000 points in the real space sphere ( `ROPT`= 1.0)`PREC= Normal`1000 points in the real space sphere ( `ROPT`= 1.0)`PREC= Accurate`1000 points in the real space sphere ( `ROPT`= 1.0)`PREC= High`1500 points in the real space sphere ( `ROPT`= 1.5)

`LREAL=A`the defaults are:`PREC= Low``ROPT`=-1E-2`PREC= Med``ROPT`=-2E-3`PREC= Normal``ROPT`=-5E-4`PREC= Accurate``ROPT`=-2.5E-4`PREC= High``ROPT`=-4E-4

This behaviour can be overwritten by specifying the option

`ROPT`in the INCAR file. For mixed atomic species we, in fact, strongly recommend to use`LREAL=A`(see section 6.39).

`PREC=Accurate` avoids wrap around errors and uses an augmentation grid
that is exactly twice as large as the coarse grid for the representation
of the pseudo wavefunctions. `PREC=Accurate` increases the memory requirements somewhat,
but it should be used if very accurate forces (phonons and second derivatives) are required.
The accuracy of forces can be further improved by specifying `ADDGRID = .TRUE.` (see Sec. 6.63).

**New manual entry for PREC=High:**

The use of

**Old manual entry for PREC=High:**

N.B. Requests for support are to be addressed to: vasp.materialphysik@univie.ac.at