[Pw_forum] Different optical mode frequency at the same q-vector

Kyeong-hyun Park kpark39 at illinois.edu
Mon Oct 15 07:24:51 CEST 2012

Dear Dr. Lorenzo Paulatto and other users

First of all, thank you for your advice.

I have kept trying to figure out the problems by setting 'epsil=true' in '
ph.in' and hard-coding 'lo_to_split=false' in 'matdyn.f90',
but the results were still the same, and I even wonder if 'lo_to_split'
played any roll in my simulation.

I also looked into other input files, but I didn't find anything
suspicious. What's in my mind is that the frequencies should be
reasonably continuous even if the structure defined in my code were not
perfectly same as the targeting material. I am still seeking for any advice.

Meanwhile, I will try different 'K_POINTS' setup in 'scf.in' that have been
set as 'automatic 4 4 4 0 0 0'
I thought '4 4 4 0 0 0' would be okay for most of structures even though it
will take longer time due to not pre-defined symmetry points.
I will give it a shot with '6 6 6 0 0 0'. Please let me know if you have
any better suggestion.
For the structure like rhombohedron, should it be some thing like '4 4 6 0
0 0' ?

Thank you.

Best Regards,

On Fri, Oct 12, 2012 at 11:48 AM, Lorenzo Paulatto <
lorenzo.paulatto at impmc.upmc.fr> wrote:

> On 12 October 2012 01:14, Kyeong-hyun Park <kpark39 at gmail.com> wrote:
>> To manage LO-TO splitting, I also set 'epsil=true'. That's pretty much what I have in my input files.
>> I hope this is enough description to get a meaningful help. Any advice will be appreciated. Thank you.
> I'm happy that you managed to write back.. I think your answer pretty much
> solves the problem: if you use LO-TO splitting than the optical phonons
> frequency at Gamma will depends on the direction. matdyn.x defines this
> direction depending on the point that precedes Gamma in its list of
> q-points.
> If for some specific reason, you do not want the splitting to be computes,
> you could open matdyn.f90 and hard-code lo_to_split to be .FALSE., or edit
> the dynamical matrix file and remove the value Z*
> --
> Dr. Lorenzo Paulatto
> IdR @ IMPMC -- CNRS & Université Paris 6
> phone: +33 (0)1 44275 084 / skype: paulatz
> www:   http://www-int.impmc.upmc.fr/~paulatto/
> mail:  23-24/4é16 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 05
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