ABINIT Discussion Forums

I have been going through tutorespn tutorials and simply trying to compute frequencies at Gamma point of b-SiC. If anyone has done it successfully could you please share the wisdom. RF2 tutorial fails to produce the out file with frequencies and it is too complicated. I get lost in changing the variables and still not getting flawless calculations.

Thank you!

N

Dear nbod,

it is very hard to guess where the problem is, without your input and output files. You should at least attach them.

Also, you could put an effort to read through the rest of the forum. I think there are many similar (solved) problem there. If you don't find any, you could search through the old mailing list (available on the abinit web site). I'm almost certain that you'll find your answers there.
Furthermore, if you lack some theory, please, regard first the references mentioned in the RF tutorial. And read the netiquette.

I hope that this will set you up on the right path.

Cheers!

Igor L.

Dear Igor, thank you for your reply. Since then i have been able get phonon dispersion curve for b-SiC. Now I am trying some other structures - cryt-SiO2. After generating DDB files and combining them together, the following step of computing interatomic force constants gives me the following error:
symdm9 : ERROR -
Informations are missing in the DDB.
The dynamical matrix number 22 cannot be built,
since no blok with wavevector 2.500000E-01 2.500000E-01 2.500000E-01
has been found.
Action : add the required blok in the DDB, or modify your input file.

I assume I need to change my very first input file trf2_1.in? or trf2_4.in?

here is my trf2_1.in input file:
#Sets 4-10 : 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 2 # 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 3-10

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

#Definition of the unit cell
acell 7.135 7.135 7.135 angstrom
angdeg 90 90 90
chkprim 0
#rprim
# 0.0 0.5 0.5 # In lessons 1 and 2, these primitive vectors
# 0.5 0.0 0.5 # (to be scaled by acell) were 1 0 0 0 1 0 0 0 1
# 0.5 0.5 0.0 # that is, the default.

#Definition of the atom types
ntypat 2 # There are two types of atom
znucl 14 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. Here, type 1 is the Aluminum,
# type 2 is the Arsenic.

#Definition of the atoms
natom 2 # There are two atoms
typat 1 2 # The first is of type 1 (Al), the second is of type 2 (As).

xred
0.000 0.000 0.000
0.125 0.125 0.125


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

#Exchange-correlation functional

ixc 1 # LDA Teter Pade parametrization

#Definition of the planewave basis set

ecut 12.0 # Maximal kinetic energy cut-off, in Hartree

#Definition of the k-point grid
ngkpt 4 4 4
nshiftk 4 # Use one copy of grid only (default)
shiftk 0.0 0.0 0.5 # This gives the usual fcc Monkhorst-Pack grid
0.0 0.5 0.0
0.5 0.0 0.0
0.5 0.5 0.5

#Definition of the SCF procedure
iscf 5 # Self-consistent calculation, using algorithm 5
nstep 25 # Maximal number of SCF cycles
diemac 9.0 # Although this is not mandatory, it is worth to
# precondition the SCF cycle. The model dielectric
# function used as the standard preconditioner
# is described in the "dielng" input variable section.
# The dielectric constant of AlAs is smaller that the one of Si (=12).

thank you!

Dear nbod,

yes, you should change your trf2_1.in file. Heh, but the important stuff is in the first 3 datasets, which you haven't pasted into your post. Specifically, the list of q-points to be used in the rf calculation. There are really a lot of posts here on the forum about the same problem. Here's one, for example

viewtopic.php?f=10&t=1220

On the other hand, did you go through the tutorial? Check the trf2_2.in.

Igor