Hi,
I think that the most part of the problem is that you use a k_grif_cutoff
instead of a Monkhorst_Pack grid. It means that only a gamma point is used in
the calculation. Incorporate a MP grid with values like 9 x 9 x 7 could improve
your results. Take care also of the parameters like the Meshcutoff, PAO
EnergyShift, DMNumberPulay and DMmixingWeight. A good starting point is to
optimize these values (look at the evolution of Etot for different values).
Concerning the ZnO (and all semiconductor) structures , I also have 2 questions
to the SIESTA users.
1) SIESTA (and DFT in general) reproduces band-structure with very small gap
comparing to experimental data. To overcome this fact, a rigid shift of the
gap is sometimes apply in calculation. In SIESTA's manual this shift is
controlled by the keyword Optical.Scissor. I've tested it but there is not
change when I plot the band structure and I don't know why. I think that the
values of the gap should be the sum of the calculated gap without Scissor + the
shift.
2) In the output files, there is a part concerning the results of the optical
calculation with the value of a "f-sume rule". According to the output, this
number should be closed to 1 for closed shell system but in best case I have a
value of 0.56. What is missing and how increase this value ?
I hope that my answer could help and I also thank in advance for people that
could help me for these new questions.
David Cornil
Ph.D student
Université de Mons-Hainaut
Belgium
----- Message d'origine ----
De : Ravi Agrawal <[EMAIL PROTECTED]>
À : SIESTA-L@listserv.uam.es
Envoyé le : Mardi, 21 Octobre 2008, 19h12mn 20s
Objet : [SIESTA-L] ZnO modeling
Hi,
I am trying to use SIESTA to model ZnO bulk structure. However, I ran into the
convergence issues. The dDmax value does not seem to decrease beyond a certain
value. The output looks like this:
siesta: 141 -3882.8445 -3868.6803 -3868.6946 1.5756 -3.4114
siesta: 142 -3882.8432 -3868.6789 -3868.6907 1.5591 -3.4098
siesta: 143 -3882.8447 -3868.6803 -3868.6947 1.5759 -3.4113
siesta: 144 -3882.8438 -3868.6789 -3868.6906 1.5593 -3.4097
siesta: 145 -3882.8444 -3868.6803 -3868.6946 1.5757 -3.4114
siesta: 146 -3882.8432 -3868.6789 -3868.6907 1.5592 -3.4098
siesta: 147 -3882.8447 -3868.6803 -3868.6947 1.5760 -3.4113
siesta: 148 -3882.8438 -3868.6789 -3868.6906 1.5594 -3.4097
siesta: 149 -3882.8444 -3868.6803 -3868.6946 1.5759 -3.4114
siesta: 150 -3882.8432 -3868.6789 -3868.6907 1.5594 -3.4098
siesta: 151 -3882.8447 -3868.6803 -3868.6947 1.5761 -3.4113
siesta: 152 -3882.8438 -3868.6789 -3868.6906 1.5595 -3.4097
siesta: 153 -3882.8444 -3868.6803 -3868.6946 1.5760 -3.4114
siesta: 154 -3882.8432 -3868.6789 -3868.6907 1.5595 -3.4098
siesta: 155 -3882.8447 -3868.6803 -3868.6947 1.5763 -3.4113
siesta: 156 -3882.8438 -3868.6789 -3868.6906 1.5597 -3.4097
siesta: 157 -3882.8444 -3868.6803 -3868.6946 1.5761 -3.4114
siesta: 158 -3882.8432 -3868.6789 -3868.6907 1.5596 -3.4098
siesta: 159 -3882.8447 -3868.6803 -3868.6947 1.5764 -3.4113
siesta: 160 -3882.8438 -3868.6789 -3868.6906 1.5598 -3.4097
siesta: 161 -3882.8444 -3868.6803 -3868.6946 1.5763 -3.4114
siesta: 162 -3882.8432 -3868.6789 -3868.6907 1.5598 -3.4098
siesta: 163 -3882.8447 -3868.6803 -3868.6947 1.5765 -3.4113
siesta: 164 -3882.8438 -3868.6789 -3868.6906 1.5599 -3.4097
siesta: 165 -3882.8444 -3868.6803 -3868.6946 1.5764 -3.4114
siesta: 166 -3882.8432 -3868.6789 -3868.6907 1.5599 -3.4098
siesta: 167 -3882.8447 -3868.6803 -3868.6947 1.5767 -3.4113
siesta: 168 -3882.8438 -3868.6789 -3868.6906 1.5601 -3.4097
siesta: 169 -3882.8444 -3868.6803 -3868.6946 1.5765 -3.4114
I am also copying the input file below. Any help will be appreciated.
SystemName ZnO Crystal
SystemLabel zno
NumberOfAtoms 4
NumberOfSpecies 2
MeshCutoff 500 Ry
%block ChemicalSpeciesLabel
1 30 Zn # Species index, atomic number, species label
2 8 O
%endblock ChemicalSpeciesLabel
AtomicCoordinatesFormat Ang
# c = 5.20658; a = 3.249925; u = 0.389
LatticeConstant 5.20658 Ang
#%block LatticeParameters
# 1.0811 1.0811 1.0000 90 90 60
#%endblock LatticeParameters
%block LatticeVectors
1.081139 0.000000 0.000000
0.540569 0.936294 0.000000
0.000000 0.000000 1.000000
%endblock LatticeVectors
%block AtomicCoordinatesAndAtomicSpec
ies
2.81452 1.62496 2.60329 1
2.81452 1.62496 4.62865 2
5.62904 3.24993 0.00000 1
5.62904 3.24993 2.02536 2
%endblock AtomicCoordinatesAndAtomicSpecies
kgrid_cutoff 5.0 Bohr
maxSCFIterations 200
