[Wien] band gap with EV-GGA and PBE-GGA
Gerardo Félix Martínez
gjfelix2005 at gmail.com
Thu May 24 16:14:15 CEST 2007
Hi, thanks in advance for your replies.
Is there a way to estimate the amount of error in the band gap due to de
LDA/GGA problem?
I want to calculate the band gap for GaN(1-x)P(x) with the following
structure (it is small due to my computer resources):
GaNFig
P LATTICE,NONEQUIV.ATOMS: 16
MODE OF CALC=RELA unit=ang
8.503771 8.503771 17.007542 90.000000 90.000000 90.000000
ATOM -1: X=0.00000000 Y=0.00000000 Z=0.00000000
MULT= 1 ISPLIT= 8
Ga1 NPT= 781 R0=0.00010000 RMT= 1.9500 Z: 31.0
LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
0.0000000 1.0000000 0.0000000
0.0000000 0.0000000 1.0000000
ATOM -2: X=0.00000000 Y=0.00000000 Z=0.50000000
MULT= 1 ISPLIT= 8
Ga2 NPT= 781 R0=0.00010000 RMT= 1.9500 Z: 31.0
LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
0.0000000 1.0000000 0.0000000
0.0000000 0.0000000 1.0000000
ATOM -3: X=0.50000000 Y=0.50000000 Z=0.00000000
MULT= 1 ISPLIT= 8
Ga3 NPT= 781 R0=0.00010000 RMT= 1.9500 Z: 31.0
LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
0.0000000 1.0000000 0.0000000
0.0000000 0.0000000 1.0000000
ATOM -4: X=0.50000000 Y=0.50000000 Z=0.50000000
MULT= 1 ISPLIT= 8
Ga4 NPT= 781 R0=0.00010000 RMT= 1.9500 Z: 31.0
LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
0.0000000 1.0000000 0.0000000
0.0000000 0.0000000 1.0000000
ATOM -5: X=0.50000000 Y=0.00000000 Z=0.25000000
MULT= 1 ISPLIT= 8
Ga5 NPT= 781 R0=0.00010000 RMT= 1.9500 Z: 31.0
LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
0.0000000 1.0000000 0.0000000
0.0000000 0.0000000 1.0000000
ATOM -6: X=0.50000000 Y=0.00000000 Z=0.75000000
MULT= 1 ISPLIT= 8
Ga6 NPT= 781 R0=0.00010000 RMT= 1.9500 Z: 31.0
LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
0.0000000 1.0000000 0.0000000
0.0000000 0.0000000 1.0000000
ATOM -7: X=0.00000000 Y=0.50000000 Z=0.25000000
MULT= 1 ISPLIT= 8
Ga7 NPT= 781 R0=0.00010000 RMT= 1.9500 Z: 31.0
LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
0.0000000 1.0000000 0.0000000
0.0000000 0.0000000 1.0000000
ATOM -8: X=0.00000000 Y=0.50000000 Z=0.75000000
MULT= 1 ISPLIT= 8
Ga8 NPT= 781 R0=0.00010000 RMT= 1.9500 Z: 31.0
LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
0.0000000 1.0000000 0.0000000
0.0000000 0.0000000 1.0000000
ATOM -9: X=0.25000000 Y=0.25000000 Z=0.12500000
MULT= 1 ISPLIT= 8
N 1 NPT= 781 R0=0.00010000 RMT= 1.7000 Z: 7.0
LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
0.0000000 1.0000000 0.0000000
0.0000000 0.0000000 1.0000000
ATOM -10: X=0.25000000 Y=0.25000000 Z=0.62500000
MULT= 1 ISPLIT= 8
N 2 NPT= 781 R0=0.00010000 RMT= 1.7000 Z: 7.0
LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
0.0000000 1.0000000 0.0000000
0.0000000 0.0000000 1.0000000
ATOM -11: X=0.75000000 Y=0.75000000 Z=0.12500000
MULT= 1 ISPLIT= 8
N 3 NPT= 781 R0=0.00010000 RMT= 1.7000 Z: 7.0
LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
0.0000000 1.0000000 0.0000000
0.0000000 0.0000000 1.0000000
ATOM -12: X=0.75000000 Y=0.75000000 Z=0.62500000
MULT= 1 ISPLIT= 8
N 4 NPT= 781 R0=0.00010000 RMT= 1.7000 Z: 7.0
LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
0.0000000 1.0000000 0.0000000
0.0000000 0.0000000 1.0000000
ATOM -13: X=0.75000000 Y=0.25000000 Z=0.37500000
MULT= 1 ISPLIT= 8
N 5 NPT= 781 R0=0.00010000 RMT= 1.7000 Z: 7.0
LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
0.0000000 1.0000000 0.0000000
0.0000000 0.0000000 1.0000000
ATOM -14: X=0.75000000 Y=0.25000000 Z=0.87500000
MULT= 1 ISPLIT= 8
N 6 NPT= 781 R0=0.00010000 RMT= 1.7000 Z: 7.0
LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
0.0000000 1.0000000 0.0000000
0.0000000 0.0000000 1.0000000
ATOM -15: X=0.25000000 Y=0.75000000 Z=0.37500000
MULT= 1 ISPLIT= 8
N 7 NPT= 781 R0=0.00010000 RMT= 1.7000 Z: 7.0
LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
0.0000000 1.0000000 0.0000000
0.0000000 0.0000000 1.0000000
ATOM -16: X=0.25000000 Y=0.75000000 Z=0.87500000
MULT= 1 ISPLIT= 8
N 8 NPT= 781 R0=0.00010000 RMT= 1.7000 Z: 7.0
LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
0.0000000 1.0000000 0.0000000
0.0000000 0.0000000 1.0000000
1 NUMBER OF SYMMETRY OPERATIONS
1 0 0 0.0000000
0 1 0 0.0000000
0 0 1 0.0000000
1
This structure file was done with supercell duplicating in the Z direction
only.
I've done the calculations for x=0,.25,.5,.75,1, and the results agrees (in
the curve form) with another predictions like tight binding. But the problem
is that the values of energy seems low compared with these other
calculations, and with experimental results in the extreme values (GaN and
GaP). Is this due to the LDA/GGA problem? Or it can be another factors?.
Thanks a lot.
-----Original Message-----
From: wien-bounces at zeus.theochem.tuwien.ac.at
[mailto:wien-bounces at zeus.theochem.tuwien.ac.at] On Behalf Of Hong Jiang
Sent: jueves, 24 de mayo de 2007 02:03 a.m.
To: A Mailing list for WIEN2k users
Subject: Re: [Wien] band gap with EV-GGA and PBE-GGA
Hi,
Your problem is actually not related to which structure you use.
Usually the band gap calculated from LDA or GGA can not be taken too
seriously because of the well-known band gap problem of LDA/GGA, i.e.
the LDA/GGA band gaps are always under-estimated, and therefore for
small gap systems, LDA/GGA usually predict metallic behavior; for
transition metal oxides like MnO, FeO, CoO and NiO, even experimental
gaps are not small (~4 eV), LDA/GGA can also give zero or very small
gaps. In terms of the band gap, EV93 is known to give larger gaps, but
usually not large enough compared to experiment. For accurate and
reliable calculations of band gaps, one has to use the GW
approximation, which is unfortunately very expensive and only feasible
for small systems. See the review paper in Rep. Prog. Phys. 61, 237
(1998) for more details.
Hope this is helpful.
Hong
Mary White wrote:
> Dear R.Ahmed and all users,
> Thank you for your attention. After I first optimized the
> experimental structure (both lattice parameters and atom position), I
> calculated the band structure and got the gap of 0.2ev with EV-GGA
> (0.1ev with the experimental structure EV-GGA). The optimized lattice
> parameters is a little overestimated compared the experimental lattice
> parameters. But I found the force on the two atoms is a little large.
> So I optimized the atom position in min_lapw (not for lattice
> parameters).The force is small. Then I calculate the band gap with the
> new optimized structure, but very strange,the gap is disappear. That
> appears metallic. I don't know what I can do. Only optimized the atom
> position,the result is very different (compared with the first
> optimized structure 0.2ev).I think the optimized structure is ok.
> There is no experimental band structure. I don't know how to
> deal with it. I tried to adjust the parameters,but that is no effect.
> Any comments do help me.Thanks in advance.
>
> */Rashid Ahmed <rasofi at hotmail.com>/* wrote:
>
> Dear Mary
> hi
> This is known fact that GGA usually overestimates lattice
> parameters which susequently decrease band gap value. As your
> result with experimental lattice parameters is already very small.
> so with further decrease in band gap, it shows wrong mettalic band
> structure.
> bye
> R. Ahmed
>
>
------------------------------------------------------------------------
> From: /Mary White <us.white at yahoo.com>/
> Reply-To: /A Mailing list for WIEN2k users
> <wien at zeus.theochem.tuwien.ac.at>/
> To: /wien2k <wien at zeus.theochem.tuwien.ac.at>/
> Subject: /[Wien] band gap with EV-GGA and PBE-GGA/
> Date: /Tue, 22 May 2007 05:10:18 -0700 (PDT)/
>
> Dear all users,
>
> I calculated the energy band with EV-GGA and PBE-GGA.
> The system is semiconductor.And the gap I calculated with the
> experimental structure is about 0.1ev with EV-GGA.But when I
> calculate with the optimized structure,the gap is
> disappear.From the band structure,it appears
> metallic.The band from EV-GGA and PBE-GGA seems very
> similar.The parameters in the calculation with experimental
> structure is the same as that with optimized structure.I think
> the optimized structure is OK. I am puzzled with that.
>
> Does anyone know it? Look forward to your advice. Any
> help will be appreciated.Thank you in advance.
>
>
>
> Mary White
>
>
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