meta-GGAs

Default | ||

METAGGA |
= | none |

`METAGGA`= TPSS, RTPSS, or M06L

The implementation of the TPSS and RTPSS (revised-TPSS) selfconsistent meta-generalized gradient approximation within the projector-augmented-wave method in VASP is discussed by Sun*et al.*[158] For details on the M06-L functional read the paper of Zhao and Truhlar. [159]

`METAGGA`= MBJ

The modified Becke-Johnson exchange potential in combination with L(S)DA-correlation [160,161] yields band gaps with an accuracy similar to hybrid functional or GW methods, but computationally less expensive (comparable to standard DFT calculations). The modified Becke-Johnson potential is a local approximation to an atomic exact-exchange potential plus a screening term and is given by:

where and are two free parameters, that may be set by means of the`CMBJA`and`CMBJB`tags, respectively. The defaults of (dimensionless) and were chosen such that for a constant electron density roughly the LDA exchange is recovered. Alternatively one may also set the parameter directly, by means of the`CMBJ`-tag:`CMBJ`= [real (array)] (Default:`CMBJ`= calculated selfconsistently)The

`CMBJ`tag can be set in the following ways:- One may specify one entry per atomic type
CMBJ = c_1 c_2 ... c_n

where the order and number is in accordance with atomic types in your`POSCAR`file. The MBJ exchange potential at a point will then be calculated using the parameter belonging to the atomic species of the atomic site nearest to . - Specify a constant
CMBJ = c

`CMBJ`is not set, it will be calculated from the density at each electronic step, in accordance with`CMBJA`and`CMBJB`, from Eq. 6.4 above:`CMBJA`= [real] (Default:`CMBJA`=),`CMBJB`= [real] (Default:`CMBJB`=).N.B.I: The MBJ functional is a

*potential-only*functional,*i.e.*, there is no corresponding MBJ exchange-correlation energy, instead is taken from L(S)DA. This means MBJ calculations can never be self-consistent with respect to the total energy, which in turn means we can not compute Hellmann-Feynman forces (*i.e.*, no ionic relaxation etc). These calculations aim solely at a description of the electronic properties, primarily band gaps.N.B.II: MBJ calculations tend to diverge for surface calculations. In the vacuum, where the electron density and kinetic energy density are (close to) zero, the functional becomes unstable.

- One may specify one entry per atomic type

**Beware**: meta-GGA calculations require `POTCAR` files that include information
on the kinetic energy density of the core-electrons.
To check whether a particular `POTCAR` contains this information, type:

grep kinetic POTCARThis should yield at least the following lines (for each element on the file):

kinetic energy-density mkinetic energy-density pseudizedand for PAW datasets with partial core corrections:

kinetic energy density (partial)