[Wien] How to get the experimental gap with mBj, PBE+U and EECE methods

[Laurence Marks]

I am quite disturbed by some aspects of this thread. Trying to adjust the
U, the C in mBJ or something else in order to get a better "fit" to the
band gap verges on misleading science. If you are using the band-gap as a
calibrant and then intend to look at some other property, e.g. charge
transfer or energies this is reasonable. Adjusting it to fit experiment and
then saying that DFT & experiment agree is not something I would allow any
of my students to do.

Some careful thinking is needed, and the same criteria used in experiments
should be used in DFT. It is valid to adjust a parameter "A" using some
dataset "B" (band-gap, heats of formation etc) in order to then fix "A" and
subsequently calculate some other property "C". If "B" and "C" overlap,
this is not valid and verges on misleading science.

On Wed, Nov 23, 2016 at 5:52 AM, tran at theochem.tuwien.ac.at <
tran at theochem.tuwien.ac.at> wrote:

> I don't understand. In a previous email you mentioned an experimental
> gap of 0.1 eV, and now you want to approach 1 eV. So, what is the
> experimental value?
>
> FT
>
> On Wednesday 2016-11-23 12:40, Abderrahmane Reggad wrote:
>
> >Date: Wed, 23 Nov 2016 12:40:55
> >From: Abderrahmane Reggad <jazairdz at gmail.com>
> >Reply-To: A Mailing list for WIEN2k users <wien at zeus.theochem.tuwien.ac.
> at>
> >To: "wien at zeus.theochem.tuwien.ac.at" <wien at zeus.theochem.tuwien.ac.at>
> >Subject: Re: [Wien] How to get the experimental gap with mBj,
> >    PBE+U and EECE methods
> >
> >To Prof Tran
> >Since the unmodified version of Beck-Johnson allows me to get 0.06 ev
> which corresponds to the value of C parameter equal to the unity (01). I
> think that to increase of
> >this value would improve the gap value to 1 ev.
> >
> >The question is: Which value for C parameter shall I use to get this gap
> value?
> >
> >Best regards
> >
> >--
> >Mr: A.Reggad
> >Laboratoire de Génie Physique
> >Université Ibn Khaldoun - Tiaret
> >Algerie
> >
> >
> >
> >




-- 
Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what nobody
else has thought", Albert Szent-Gyorgi
www.numis.northwestern.edu ; Corrosion in 4D: MURI4D.numis.northwestern.edu
Partner of the CFW 100% program for gender equity, www.cfw.org/100-percent
Co-Editor, Acta Cryst A
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