The ABINIT Users Mailing List ( CLOSED )

[<pascal.boulet@univ-provence.fr>]

Dear abinit users,

First, sorry for this lengthy post!

I'm trying to calculate phonon dispersion curve and plot the result using
band2eps, but I can't succeed.

The structure is that of Mg2Si (3 atoms/cell, Fm -3 m #225). As with AlAs (F-4
3 m #216) in the tutorial, it is a FCC structure so I expected the input files
to be the same. Is this right?

So, first I calculated the phonons frequencies at 31 q points + g point. The
frequencies seem to be OK when I compare with literature data.

Now I'd like to compute the dispersion curve. I used trf2_5 files as such for
Mg2Si. In this input file, there are several things I don't understand:
1- If I'm right, at this point abinit interpolates (using the DDB file) the
dispersion curve between the k-points provided in the trf2_5 file. But how is
it possible that none of the 31 k-points used to build the DDB are listed 
among
those (71) of the trf2_5.in file? In other words, in this case, how is it
possible to make an interpolation?
2- How are these 71 k-points generated, and in particular, those between the
special k-points (G, X,L,W,...) ? Is there a rule? a program package? Any
information (textbook or web link) would be appreciated.
3- If I compare with the phonon dispersion curve published in the literature,
the path to draw the curve is different to that proposed in trf2_5.in:
W-L-G-X-W-K vs G-K-X-G-L-X-W-L, respectively. Again, is there a rule to follow
a particular path dictated by the symmetry or are we free to choose any path?

Now to create the eps file with band2eps, I also tried to use trf2_6 files as
such. But it's not working at all. The frequencies are just wrong (not 
relevant
to those in the output file of abinit, obviously downshifted so there are
negative frequencies). 

Now, I have 2 questions about trf2_6.in:
1- on the first line, is it the number of atoms/cell or the number of type of
atoms? (for Mg2Si: setting "2" works whereas "3" fails).
2- How do you set the scale factor for each line?

I would really appreciate advices. Thank you in advance for your help and 
time.

Best Regards
Pascal