by **Lantao** » Wed May 06, 2015 11:14 pm

Finally, someone come to reply me. Thanks.

Actually, with more empty bands taken into account, the gap shows between the 18th and 19th band. This is a good news.

On the other hand, even I did a careful convergence analysis, I still can not have the good results.

I can even have a negative gap which is not at all logic.

Help me please. And here's the input file.

# ZnO : Calculation of the GW corrections

# Dataset 1 : ground state calculation

# Dataset 2 : calculation of the KSS file

# Dataset 3 : calculation of the screening (epsilon^-1 matrix for W)

# Dataset 4 : calculation of the self-Energy matrix elements (GW corrections)

# In the first tutorial of GW calculation, we checked the convergence so that we know

# for the Self-Energy computation, we need ecutwfn = 5.0 ecutsigx = 6.0 nband = 100

# for screening computation, we need ecutwfn = 4.0 ecuteps = 6.0 nband = 100

# The program broke after 3 datasets

#ndtset 4

# restartxf -2 # RESTART from (X,F) history

# restartxf=-2 :Read the HIST file and select the atomic

# positions and cell parameters with the lowest energy

# use restartxf=-1 or -2 to restart a calculation that was not completed

############# Usual self-consistent ground-state calculation ###############

#nshiftk1 1

#shiftk1 0.0 0.0 0.5

#istwfk1 *0

#prtden1 1

################################################################################

######## Definition of parameters for the calculation of the KSS file ########

#iscf2 -2

#getden2 -1

#nbandkss2 -1 # This lead to the generation (full diagonalization of the KS

# hamiltonian) and storage of the maximum possible number of states

# (or bands) common to all points.

#kssform2 1 # The value 1 corresponds to ask a KSS through a diagonalization

# of the KS hamiltonian.

#nband2 150

#nbdbuf2 120

################################################################################

############## Calculation of the screening (epsilon^-1 matrix) ############

#optdriver3 3 # Screening calculation

#getkss3 -1 # Obtain KSS file from previous dataset

#nband3 150

#ecutwfn3 30.0 # Cut-off energy of the planewave set to represent

# the wavefunctions. It would be more convenient to keep

# the default ecut value.

#ecuteps3 40.0 # Cut-off energy of the planewave set to represent

# the dielectric matrix.

#ppmfrq3 16.7 eV # Imaginary frequency where to calculate the screening

#nbdbuf3 120

################################################################################

##### Calculation of the Self-Energy matrix elements (GW corrections) ######

optdriver 4 # Self-Energy calculation

getkss -1 # Obtain KSS file from dataset 1

getscr -1 # Obtain SCR file from previous dataset

nband 150 # Bands to be used in the Self-Energy calculation

nbdbuf 120

ppmfrq 16.7 eVecutwfn 30.0 # Planwaves to be used to present the wavefunctions.

# It would be more convenient to keep the default ecut value.ecutsigx 40.0 # Dimension of the G sum in Sigma-x.

# It would be better to keep the default ecut value.

nkptgw 1 # number of k-point where to calculate the GW correction

kptgw # k-point

0.000 0.000 0.000

bdgw 18 19 # calculate GW corrections for bands from 4 to 5

################################################################################

# Data common to the three different datasets

##################### Definition of the atom types #####################

ntypat 2 # There are two types of atoms

znucl 30 8 # The keyword "znucl" refers to the atomic number of the

# possible type(s) of atom. The pseudopotential(s)

# mentioned in the "files" file must correspond

# to the type(s) of atom.

natom 4 # There are 4 atoms per cell

typat 1 2 # 1 Zn atoms (first type), 1 O atom (second type)

spgroup 186

spgaxor 1

spgorig 1

brvltt -1 # assign brvltt from the space group information

natrd 2 # number of atom read

xred # Definition of the primitive cell

1./3 2./3 1.0951595455E-04 # Position of Zn

1./3 2./3 3.7989048405E-01 # O

acell 6.2633392923E+00 6.2633392923E+00 1.0083776580E+01 Bohr #and scale of Cartisien Coordinate

#In unit of angstrom 1Bohr=0.5291772108 Anstrong

rprim

1.0000000000E+00 4.2710751043E-37 -7.9295776162E-37

-5.0000000000E-01 8.6602540378E-01 0.0000000000E+00

6.1232339957E-17 1.0605752387E-16 1.0000000000E+00

############################################################################

##################### Definition of the k-point grid ###################

ngkpt 5 5 3

nshiftk 1

shiftk

0.0 0.0 0.0

# 0.0 0.0 0.5

#kptrlatt

# 17 0 0

# 0 17 0

# 0 0 11

#shiftk 0.0 0.0 0.0 # When the primitive vectors of the lattice do NOT form a FCC

# or a BCC lattice, we usually use nshiftk = 1 and

# shiftk 0.5 0.5 0.5.

istwfk *1 # This is mandatory in all the GW steps

symmorphi 1

############################################################################

################ Exchange-correlation functional ##############

ixc 11 # GGA, Perdew-Burke-Ernzerhof GGA function

# pawecutdg 80 # PAW-Energy Cutoff for the double grid

timopt 2

##################################################################

############### Definition of the SCF procedure ################

nstep 100 # Maximal number of SCF cycles

iscf 17

ecut 60.0 # Maximal kinetic energy cut-off, in Hartree

tolwfr 1.0d-10

##################################################################

And here's the result in my output file:

=== KS Band Gaps ===

>>>> For spin 1

Minimum optical gap = 0.6651 [eV], located at k-point : 0.0000 0.0000 0.0000

Fundamental gap = 0.6651 [eV], Top of valence bands at : 0.0000 0.0000 0.0000

Bottom of conduction at : 0.0000 0.0000 0.0000

SIGMA fundamental parameters:

PLASMON POLE MODEL 1

number of plane-waves for SigmaX 4127

number of plane-waves for SigmaC and W 4127

number of plane-waves for wavefunctions 2719

number of bands 150

number of independent spin polarizations 1

number of spinorial components 1

number of k-points in IBZ 10

number of q-points in IBZ 10

number of symmetry operations 12

number of k-points in BZ 75

number of q-points in BZ 75

number of frequencies for dSigma/dE 9

frequency step for dSigma/dE [eV] 0.25

number of omega for Sigma on real axis 0

max omega for Sigma on real axis [eV] 0.00

zcut for avoiding poles [eV] 0.10

EPSILON^-1 parameters (SCR file):

dimension of the eps^-1 matrix on file 4127

dimension of the eps^-1 matrix used 4127

number of plane-waves for wavefunctions 2719

number of bands 150

number of q-points in IBZ 10

number of frequencies 2

number of real frequencies 1

number of imag frequencies 1

matrix elements of self-energy operator (all in [eV])

Perturbative Calculation

k = 0.000 0.000 0.000

Band E0 <VxcLDA> SigX SigC(E0) Z dSigC/dE Sig(E) E-E0 E

18 -2.174 -22.729 -26.479 4.905 0.741 -0.349 -21.873 0.856 -1.318

19 -1.509 -12.023 -8.581 -3.198 0.798 -0.253 -11.829 0.194 -1.315

E^0_gap 0.665

E^GW_gap 0.003

DeltaE^GW_gap -0.662