`ISMEAR` = -5 | -4 | -3 | -2 | 0 | N
`SIGMA`= [real] `FERWE`= [real array]
`FERDO`= [real array]

Default | ||

ISMEAR |
= | 1 |

SIGMA |
= | 0.2 |

`ISMEAR` determines how the partial occupancies
are set for each
orbital. For the finite temperature LDA `SIGMA` determines the
width of the smearing in eV.

`ISMEAR`:

- Fermi-smearing
- 0
- Gaussian smearing
- 1..
- method of Methfessel-Paxton order .
*Mind:*For the Methfessel-Paxton scheme the partial occupancies can be negative. - partial occupancies are read in from WAVECAR (or INCAR), and kept
fixed throughout run.
If the occupancies are fixed by you, there should be a tag

FERWE = f1 f2 f3 ... f(NBANDS)

and for spin-polarized calculationsFERDO = f1 f2 f3 ... f(NBANDS)

in the INCAR file supplying the partial occupancies for all bands and k-points. The band-index runs fastest. The partial occupancies must be between 0 and 1 (for spin-polarized and non-spin-polarized calculations).*Mind:*Partial occupancies are also written to the OUTCAR file, but in this case they are multiplied by 2, i.e. they are between 0 and 2. - perform a loop over smearing-parameters supplied in the
INCAR file. In this case a tag
SMEARINGS= ismear1 sigma1 ismear2 sigma2 ...

must be present in the INCAR file, supplying different smearing parameters.`IBRION`has to be set to -1 and`NSW`to the number of supplied values (ismear) . The first loop is done using the tetrahedron method with Blöchl corrections. - tetrahedron method without Blöchl corrections (use a -centered k-mesh, see sec.5.5 )
- tetrahedron method with Blöchl corrections (use a -centered k-mesh, see sec.5.5 )

The method of Methfessel-Paxton (MP) also results in a very accurate
description of the total energy, nevertheless the width of the
smearing (`SIGMA`) must be chosen carefully
(see also 7.4). Too large smearing-parameters might result
in a wrong total energy, small smearing parameters
require a large k-point mesh. `SIGMA` should be as large as possible keeping
the difference between the free energy and the total energy
(i.e. the term '`entropy T*S`') in the OUTCAR file negligible (1 meV/atom).
In most cases and leads to very similar results.
The method of MP is also the method of choice for large supercells, since
the tetrahedron method is not applicable, if less than three k-points are used.

*Mind:* Avoid using `ISMEAR`0 for semiconductors and insulators,
since this often leads to incorrect results (The occupancies of
some states might be larger or smaller than 1). For insulators use `ISMEAR`=0
or `ISMEAR`=-5.

The Gaussian smearing (GS) method also leads to reasonable results in most
cases.
Within this method it is necessary to extrapolate from
finite `SIGMA` results to `SIGMA`=0 results. You can find an extra line
in the OUTCAR file '`energy( SIGMA )`' giving the extrapolated
results.
Large `SIGMA` values lead to a similar error as
the MP scheme, but in contrast to the MP scheme
one can not determine how large the error due to the smearing is with
systematically reducing `SIGMA`.
Therefore the method of MP is more convenient than the
GS method. In addition, in the GS method forces and the stress tensor
are consistent with the free energy and not the energy for `SIGMA` 0.
Overall the Methfessel-Paxton method is easier to use for metallic systems.

For further considerations on the choice for the smearing method see sections 7.4,8.6. To summarize, use the following guidelines:

- For semiconductors or insulators use the tetrahedron
method (
`ISMEAR`=-5), if the cell is too large (or if you use only a single or two k-points) use`ISMEAR`=0 in combination with a small`SIGMA`=0.05. - For relaxations
*in metals*always use`ISMEAR`=1 or`ISMEAR`=2 and an appropriate`SIGMA`value (the entropy term should be less than 1 meV per atom).*Mind:*Avoid to use`ISMEAR`0 for semiconductors and insulators, since it might cause problems.For metals a sensible value is usually

`SIGMA= 0.2`(which is the default). - For the calculations of the DOS and very accurate
*total energy*calculations (no relaxation in metals) use the tetrahedron method (`ISMEAR`=-5).