The ABINIT Users Mailing List ( CLOSED )

[<ilukacevic@fizika.unios.hr>]

Dear abinit users,

I am having some problems while trying to reproduce the bandstructure of VN in
its metallic rocksalt phase at ambient pressure (C. Stampfl, PRB 63, 155106
(2001)). Specifically, I cannot calculate the closed bands at X point. I 
always
get a finite opened gap.
I am using abinit 5.4.4p, LDA psps from the website and the following input
file:


# VN rocksalt phase
#
# Computation of the band structure at about 0 GPa
# First, a SCF density computation, then a non-SCF band structure calculation.

ndtset 2

#Dataset 1 : usual self-consistent calculation
kptopt1 1          # Option for the automatic generation of k points,
                   # taking into account the symmetry
nshiftk1 4
shiftk1  0.5 0.5 0.5  # These shifts will be the same for all grids
         0.5 0.0 0.0
         0.0 0.5 0.0
         0.0 0.0 0.5
ngkpt1   3*6
prtden1  1         # Print the density, for use by dataset 2
toldfe1  1.0d-8
nband1   10

#Dataset 2 : the band structure
iscf2    -2
getden2  -1
kptopt2  -6
nband2   10
ndivk2   15 7 12 15 15 12 # 15, 7, 12, 15, 15 and 12 divisions of 6 segments,
delimited
                          # by 7 points
kptbounds2  0.0 0.0  0.0  # Gamma
            0.5 0.0  0.5  # X
            0.5 0.25 0.75 # W
            0.5 0.5  0.5  # L
            0.0 0.0  0.0  # Gamma
            0.5 0.5  1.0  # K
            0.5 0.0  0.5  # X

tolwfr2  1.0d-12
occopt   4
tsmear   0.04

iprcel   45
npulayit 10
nline    8
nnsclo   4

#Definition of the unit cell
acell    3*7.97
angdeg   90  90  90
spgroup  225
brvltt  -1

#Definition of the atom types
ntypat   2
znucl    23 7

#Definition of the atoms
natom 2           # There are two atoms
typat 1 2         # They both are of type 1, that is, Silicon.
xred              # This keyword indicate that the location of the atoms
                  # will follow, one triplet of number for each atom
   0.0  0.0  0.0  # Triplet giving the REDUCED coordinate of atom 1.
   1/2  1/2  1/2  # Triplet giving the REDUCED coordinate of atom 2.

#Definition of the planewave basis set
ecut 48           # Maximal kinetic energy cut-off, in Hartree

#Definition of the SCF procedure
nstep 100         # Maximal number of SCF cycles



I have tried to increase GS ngkpt (after 3*12 results don't change anymore),
nband (12 gives the same results as 10) and DS2 tolwfr (10^-16 gives the same
as 10^-12), but without success to close the gap. I am aware of the LDA
inappropriatness, but I thought that at least it would give the correct nature
of the crystal.

I would appreciate any tips and corrections to my calculations.

Thank you in advance!

Igor Lukacevic