I'm not sure why you get the error you get, supercell calculations cause
every kind of problems with symmetry. However, something easy and quick
you can do, is to generate the dynamical matrix of the super-cell
starting from a unit cell calculation with matdyn. All you have to do a
unit-cell phonon calculation and that feed matdyn and input like this:
&input
flfrc='mat2R'
asr='crystal'
q_in_cryst_coord = .true.
l1=2
l2=2
l3=2
fldyn='sc222_dyn'
/
1
0 0 .5
Where l1,l2 and l3 specify the size of the supercell. You can also
specify the supercell as at=a1x,a1y,...a3y,a3z which should allow you to
go from FCC to SC.
The resulting dynamical matrix file does not contain the header, but
this can easily be solved adding a line like this
CALL write_dyn_mat_header( filout, ntyp, nat, ibrav, nspin_mag, &
celldm, at, bg, omega, atm, amass, tau,ityp,m_loc,nqq)
just before the call to write_dyn_on_file, line 621 of matdyn.x
hth
On 3/18/20 2:06 PM, Antoine Jay wrote:
Dear all,
I ckecked the phonon frequencies at q=gamma of a 512-atoms cubic
supercell of bulk silicon. (kpoint=gamma also)
As the phonon code output the "wrong representation" error, I added
nosym and noinv.
The output frequencies seem to be right (80-507cm^-1) except for the
last one that is 1132cm^-1
Hopefully, a simple ASR was enough to decrease this frequency down to
507cm^-1.
This calcul implies three questions:
1) How is it possible to have such a decrease between before ASR and
after ASR, is the calcul wrong (input in PJ)?
2) Why is there a "wrong representation" error, whereas the atomic
coordinates are exactelly symetric and not quasi-symetric?
3) Is it possible to know which modes are degenerated (nosym implies C_1
space group which looses the symetry analysis)?
For this last, I cannot use only the phonons frequencies because they
are not exactelly equals, and due to the BZ folding in the supercell,
several frequencies are very close from each other.
Thank you very much for your help.
Antoine Jay
LAAS-CNRS
Toulouse France
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