[Wien] increase band gap with change RMT.

[Carrier, Pierre]

Hello Fred and Arash,

Thanks for referring to our preprint! Indeed we used the Wien2k code but included in it Christensen's potential [see PRB 30, 5753 (1984); or more recently, PRB 67, 165209 (2003)], i.e., a Gaussian potential X (4*pi)**1/2 can be added close to line 1122 in /SRC_lapw0/lapw0.F. In this way, the gap opens, but at the price of additional semi-empirical parameters. 

The band gap of the zinc-blende InN structure from Wien2k with the LDA (and no Gaussian potential) that we get is -0.43 eV [that is, the gap between the Gamma_15(valence) band to the Gamma_1(conduction) band]. Wurtzite-InN gives similar results.

Ciao!
Pierre 

-----Original Message-----
From: Fred Nastos [mailto:nastos at physics.utoronto.ca]
Sent: Wednesday, January 28, 2004 10:27 PM
To: wien at zeus.theochem.tuwien.ac.at; arash bouchani
Subject: Re: [Wien] increase band gap with change RMT.


On January 28, 2004 11:14 am, arash bouchani wrote:
> Dear  all  Wein2K Users
>
> We work on electronic structure of InN (III-V group of semiconductors).In
> literatures there are some different experimental values for energy gap for
> it.
>
> As follows:
>
> 1-                   Eg =0.7ev
> 2-                   Eg =1.8ev

You might want to look at a recent preprint:
	http://www.arxiv.org/abs/cond-mat/0401306
I think they even used the WIEN code.

> In computational point of view people have got values like:
> 1-emprical pseudopotential calculation Eg = 2ev
> 2-first principles treatment in the local density approximation Eg = 1.3ev
> 3-ortogonalized linear-combination of atomic orbitals(OLCAO) Eg = 1.02ev
> 4-Linear muffintin-orbitals (LMTO)  Eg = 0.26ev
> 5-full-potential linear muffin-tin orbital (FLMTO)  Eg = -0.26ev
>
> First of all we used LDA and GGA(96) approximations leading to:
>
> 1-                   Eg = 0.16 ev (for LDA)
> 2-                    Eg = 0.17ev (for GGA)
>
> Which are far from  experimental values for this reason I used
> Engle&Vosko approximation
>
> for obtaining energy gap choosing 25 in {case.in0 file}.We obtain Eg =
> 0.29975ev (with  RMT In=1.85 A and RMT N=1.75 A).
>
> As the value of Eg show still there is a discussion for Eg value.
>
> Would you kindly tell me which approximation is suitable for III-V compunds
> semiconductors specially InN?

LDA band gap "problems" have been thoroughly discussed.  Look in the
archives.  In short, the LDA is not suitable for band gaps, and you shouldn't
expect it to be.

> As for as know changing the RMT values (whit no error ) in any run(by
> Engle&Vosko approximation) would not effect in Eg values.But I got
> several values for Eg by choosing different values for RMT as follow:
>
>      1-  RMT In = 1.85 A
>    RMT  N = 1.75 A  , Eg = 0.29975ev
>
>       2-RMT In = 2 A
>    RMT N = 1.7 A ,  Eg = 0.33221ev
>
>      3-RMT In = 2.2 A
>     RMT N = 1.7 A ,  Eg = 0.32423ev
>
> Can you please tell me why we have got different values of Eg for various
> RMT ?

RMT is a numerical parameter.  As is well documented, using similar RMT
values for the different atoms helps reduce errors.  If I had to guess, I 
would guess that your first value in the above list is most accurate.

>  thankyou -Arash bouchani.

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