# [Pw_forum] Problem in phonon-5.0.2

Lin, Yangzheng ylin at carnegiescience.edu
Thu Sep 4 17:57:32 CEST 2014

```Dear all QE users,

Although phonon-5.1 is available now, I have to use phonon-5.0.2 for some
other codes I am using were built on phonon-5.0.2.

Recently I found some problem that phonon-5.0.2 did not give the same
phonon frequencies as phonon-5.1 for some q points of my system. The
difference is big. For example,

Phonon-5.1 gave
q = (    0.000000000   0.000000000   0.053115094 )
**************************************************************************
freq (    1) =       3.205949 [THz] =     106.938946 [cm-1]

but Phonon-5.0.2 gave
q = (    0.000000000   0.000000000   0.053115094 )
**************************************************************************
omega( 1) =      -7.856216 [THz] =    -262.055171 [cm-1]

I found some codes in phonon-5.0.2 were modified by phonon-5.1 in
subroutine smallg_q (xq, modenum, at, bg, nrot, s, ftau, sym, minus_q)

phonon-5.0.2 used
if (.not.minus_q) then
raq = - raq
minus_q = eqvect (raq, aq, zero, accep)
endif

phonon-5.1 modified it as
if (sym(irot).and..not.minus_q) then
raq = - raq
minus_q = eqvect (raq, aq, zero, accep)
endif

So I did this modification in phonon-5.0.2 and the modified phonon-5.0.2
gave the same phonon frequencies as those from phonon-5.1 for the same q
point.

Since I have to continue use phonon-5.0.2 now, my question is does anyone
of you know if there were some other problems found in phonon-5.0.2? Thanks.
Sincerely,
Yangzheng Lin
Postdoctoral Associate
Geophysical Laboratory, Carnegie Institution for Science
5251 Broad Branch Rd. NW, Washington, DC 20015, USA
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