[Phonopy-users] FC_SYMMETRY tag with VASP

[김수란 <lor...@gm...>]

Hello

I met the non-zero acoustic mode problem at Γ point.
Acoustic modes has the finite values, 0.2~4.6 THz not almost 0.

I found that FC_SYMMTERY tag for acoustic sum rule.
It worked well.
Using FC_SYMMTERY=1, I solved the non-zero acoustic mode problem.

What I wonder is that
, in forum(
http://sourceforge.net/mailarchive/forum.php?thread_name=CAAfkA7ezXJ6ogdPLmexWH2mX-bAdes5%2B-v_0woJOB_AKwC5szQ%40mail.gmail.com&forum_name=phonopy-users
)
and the tag explanation (
http://phonopy.sourceforge.net/setting-tags.html#fc-symmetry),
FC_SYMMETRY tag does not need in VASP case because VASP imposes the sum
rule to forces.

So,
Is it okay to use FC_SYMMETRY tag for imposing acoustic sum rule even in
VASP case?
or
Should I change other parameters in INCAR of VASP for zero acoustic modes
without FC_SYMMETRY tag?

Thank you for your help.