ABINIT Discussion Forums

Your tutorial example, AlAs, is for an insulator. "This lesson aims at showing how to get the following physical properties, for an insulator ..."
What needs to be done, changed, or accounted for if I want to do a metalllic compound?
Can you supply an example?
Thanks,
JB

Hi!

The main difference is that for metals you don't have to take into account the coupling between atomic displacements and the homogeneous electric field, that exists in the case of polar insulators, for so-called "Longitudinal Optic (LO) modes". Practically that means that you don't have to do d/dk perturbation, which is needed for the el. field response. Else is the same (at least as much the RF is concerned).

For deeper understanding, please, read
X. Gonze, C. Lee, Phys. Rev. B 55, 10355 (1997).


Hope this helps,

Igor L.


Here's an example for TiSe2 in 1T phase:

# Crystalline TiSe2 - 1T phase
# computation of the response to homogeneous
# electric field and atomic displacements, at q=0
# and phonon dispersions

ndtset 9

#Set 1 : ground state self-consistency

getwfk1 0 # Cancel default
kptopt1 1 # Automatic generation of k points, taking
# into account the symmetry
nqpt1 0 # Cancel default
tolvrs1 1.0d-18 # SCF stopping criterion (modify default)
rfphon1 0 # Cancel default

#Q vectors for all datasets

#Complete set of symmetry-inequivalent qpt chosen to be commensurate
# with kpt mesh so that only one set of GS wave functions is needed.
#Generated automatically by running GS calculation with kptopt=1,
# nshift=0, shiftk=0 0 0 (to include gamma) and taking output kpt set
# file as qpt set. Set nstep=1 so only one iteration runs.

nqpt 1 # One qpt for each dataset (only 0 or 1 allowed)
# This is the default for all datasets and must
# be explicitly turned off for dataset 1.

qpt2 0.00000000E+00 0.00000000E+00 0.00000000E+00
qpt3 2.50000000E-01 0.00000000E+00 0.00000000E+00
qpt4 5.00000000E-01 0.00000000E+00 0.00000000E+00
qpt5 2.50000000E-01 2.50000000E-01 0.00000000E+00
qpt6 0.00000000E+00 0.00000000E+00 5.00000000E-01
qpt7 2.50000000E-01 0.00000000E+00 5.00000000E-01
qpt8 5.00000000E-01 0.00000000E+00 5.00000000E-01
qpt9 2.50000000E-01 2.50000000E-01 5.00000000E-01

#Sets 2-9 : Finite-wave-vector phonon calculations (defaults for all datasets)

getwfk 1 # Use GS wave functions from dataset1
kptopt 3 # Need full k-point set for finite-Q response
rfphon 1 # Do phonon response
rfatpol 1 3 # Treat displacements of all atoms
rfdir 1 1 1 # Do all directions (symmetry will be used)
tolvrs 1.0d-8 # This default is active for sets 2-9

#######################################################################
#Common input variables

#Definition of the unit cell - p = 0 GPa
acell 2*6.6388970478E+00 1.0952628882E+01
angdeg 90 90 120
spgroup 164
brvltt -1

#Definition of the atom types
ntypat 2
znucl 22 34 34

#Definition of the atoms
natom 3
typat 1 2 2
xred 0.0 0.0 0.00
1/3 2/3 0.27086866503
2/3 1/3 -0.27086866503

#Gives the number of band, explicitely (do not take the default)
nband 10
occopt 4
tsmear 0.04

#Exchange-correlation functional
ixc 1

#Definition of the planewave basis set
ecut 50
ecutsm 0.5
dilatmx 1.2

#Definition of the k-point grid
ngkpt 4 4 2
nshiftk 1
shiftk 0.5 0.5 0.5

#Definition of the SCF procedure
iscf 7
npulayit 16 # Number of Pulay iterations
nnsclo 12 # Number of non-self consistent loops
nline 14
nstep 100

timopt 2

thanks for your response.
I should have been more explicit: It is simple enough to determine the number of bands needed for a ph. calc (or any calc) for an insulator: add up all the electrons specified by the pseudoptentials and divide by 2.
What is acceptable for a metal? QE automatically adds 20% more bands I believe. Should I just do that in abinit?
tnx, jb