[Pw_forum] Phonon axsf does not move in XCrysden

[Lorenzo Paulatto]

I actually found out the "problem" (which isn't one): the displacement 
patterns are stored in the axsf as forces, which means that the atoms do not 
move but you can have an arrow on each atom pointing toward the direction of 
motion.

Click "Display -> Forces" (or tap the letter "f") to show them

hth

P.S. If you want to have the atoms moving, you 
can modify PHonon/PH/write_eigenvectors.f90, around line 230 you change:

write (iout,'(a6,1x,6f10.5)') atm(ityp(na)),  &
            a0*BOHR_RADIUS_ANGS*tau(1,na), &
            a0*BOHR_RADIUS_ANGS*tau(2,na), &
            a0*BOHR_RADIUS_ANGS*tau(3,na), &
            (DBLE(z((na-1)*3+ipol,i))/znorm,ipol=1,3)

to

write (iout,'(a6,1x,6f10.5)') atm(ityp(na)),  &
            a0*BOHR_RADIUS_ANGS*tau(:,na) &
              + factor*DBLE(z((na-1)*3+1:3,i))/znorm
            
where "factor" is the amplitude of the mode you want, I think around 0.2 is 
usually ok


On Monday, March 27, 2017 11:01:00 AM CEST Lorenzo Paulatto wrote:
> On Monday, March 27, 2017 10:18:08 AM CEST Louis Fry-Bouriaux wrote:
> > Hi Xu Huang,
> > 
> >    All I know is there is a similar question to this on the forum asked
> > 
> > recently: Lorenzo Paulatto answered the following:
> This is actually is a completely different issue, I met it myself some time
> ago.
> 
> The problem is that the axsf file does contain the displaced positions¹ but
> xcrysden does not display them. It is an xcrysden bug and I recommed you ask
> to the xcrysden mailing list², but there is a chance Tone will read this
> message here and he may have an answer.
> 
> 
> [1] Even if in DFPT the atoms are not physically displaced, we can find the
> displacement patters along which they would move (with amplitude a function
> of the temperature), that's what is saved in the axsf file, the
> displacement length set to an arbitrary value.
> 
> [2] http://www.democritos.it/mailman/listinfo/xcrysden


-- 
Dr. Lorenzo Paulatto 
IdR @ IMPMC -- CNRS & Université Paris 6
phone: +33 (0)1 442 79822 / skype: paulatz
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