Thanks a lot for replying Salvador, yes I checked mesh cut-off and
k-points, lattice constant also,
they're quite fine. As for PAO basis I pushed standard DZP down to an
exagerately low 10 meV of shift,
and still getting the same numbers, so it' s definetely converged, but
to a wrong solution.
BTW, a paper from E. Deligoz, K. Colakoglu, Y. Ciftci on Physica B
calculates CdSe bands with siesta,
using 100 Ry and of 108 k points, and TM pseudo with similar cut-off
radii, and gets good bands with 6.05 A
equilibrium lattice constant.....
It' s clearly some other problem I can not figure out,
the installation is ok as I passed all tests ok,
I' ll check better the pseudo, got it from the siesta web-site,
must be broken in some way !
Regards
Francesco
On 10/19/2012 02:57 PM, Salvador Barraza-Lopez wrote:
Hi Francesco, a couple of quick observations:
Your meshcutoff is quite low.
You are working with an insulator, so the number of k-points does not
need to be excessively large, but are you sure 4x4x4 is sufficient for
your purposes?
Your tolerance is too small, 10-5 may be enough.
You also mention your a0 is not the equilibrium one but the expt one,
yet should I assume you are comparing to a planewave code to get your
gap? if not, to what you are contrasting? You could examine if the gap
is smaller as you wish when you get the lattice constant in equilibrium.
Having said the above, the procedure you are following may be
risky... I would start with a comprehensive study of convergency of
meshcutoff, your pao.basis parameter, your a0, your k-points. Only
when all of those are converged I would go for an estimation of the
band gap. The idea is to get everything converged and then essentially
trust your final result (unless the pseudos are off, but that would be
the last thing to check on your list).
Hopefully the suggestions are helpful.
Best regards,
-Salvador
------------------------------------------------------------------------
*From:* [email protected] [[email protected]] on behalf of
Francesco Tassone [[email protected]]
*Sent:* Friday, October 19, 2012 7:07 AM
*To:* [email protected]
*Subject:* [SIESTA-L] zincblend CdSe bands
Hello, I' m trying to calculate ZB CdSe bands using TM pseudos
downloaded from the
SIESTA web. I' m doing the calculation at the exp lattice constant of
6.05 A.
I get
1. a large gap around 1.2eV (using standard CA LDA should be 0.7eV),
reducing only a bit by enlarging pao basis (e.g. energyshift to 10meV) ,
so it's not a problem of basis
2. 5 'fake' bands around -8 eV below valence band top at Gamma.
(should be deeper by about 4 eV, guess from Cd d orbitals, and quite
flatter)
LatticeConstant 6.05 Ang
%block LatticeVectors
0.500 0.500 0.000
0.000 0.500 0.500
0.500 0.000 0.500
%endblock LatticeVectors
MeshCutoff 100.0 Ry
MaxSCFIterations 50
DM.MixingWeight 0.1
DM.NumberPulay 3
DM.Tolerance 1.d-8
%block kgrid_Monkhorst_Pack
4 0 0 0.
0 4 0 0.
0 0 4 0.
%endblock kgrid_Monkhorst_Pack
SolutionMethod diagon
ElectronicTemperature 25 meV
HELP NEEDED
what am I getting wrong here, TM pseudos should be used with CA-LDA
which is default, correct ??
PS: everything ok with Si, so I guess it' s not a compilation problem.
