the electrics difference potential （ EDP） of MGGA results are trustfuL or GGA ?

[njuxyh]

Hi
I am calculated the electrics difference potential with  same interface, but I found the deltV  between  the two  atoms layer is opposite, so I am wondering the MGGA can calculate the EDP？
ps： my interface is two slab, the MGGA c parameter has fixed to some value to fitting the GW gap, and the warning of  MGGA is 
The computed TB09 meta-GGA exchange-correlation potential                    #
# diverged in   0.01 % of the simulation volume, and was                       #
# truncated to be in the range [-10.0000,  10.0000] Hartree   

so I am wounding the MGGA result for the EDP is trustful or GGA results is trustful.

[Daniele Stradi]

Hi,

the MGGA results can not be trusted for slab systems, or whatever system in which you have a vanishing electronic density.

In fact, the exchange term in the MGGA functional depends on the inverse of the electronic density, and diverges at low electronic densities. This might lead to very non-physical results. See Eq. (1) in PRL 102 226401 (2009).

Regards,
Daniele.

[njuxyh]

Hi  Daniele Stradi:

according to your states, I thought I  had a poster previous, i asked  MGGA is suitable for the transmission spectrum ?
in my two slab interface mentioned here ? one staff answer me sure,

so i am wondering if MGGA can not give trustful results for ther EDP, then MGGA can give me trustful transmission spectrum?

please help me  make me clear about this issue。


thanks very  much

[Daniele Stradi]

I just looked up the post: http://quantumwise.com/forum/index.php?topic=4307.msg19575#msg19575

MGGA is perfectly fine for transmission calculations, but should be used with cautions for system in which you have vacuum, independently on whether they are devices, slabs, etc.

Therefore, I would not use it to calculate transmission in a slab system.