[Pw_forum] Phonon dispersion with LO-TO splitting

[Barnali Bhattacharya]

Dear  Lorenzo Paulatto,

Thank you for your reply. But recently I have gone  your Physical review
paper (PHYSICAL REVIEW B *87*, 214303 (2013)
) where you have shown phonon dispersion with LO-TO splitting for graphene
(Figure 2) in page 214303-4.

"Figure 2 shows the calculated graphene phonon dispersion,
the respective anharmonic broadening and the vibrational
density of states (VDOS). The branches are labeled in the usual
way.25 There are three acoustic branches (ZA, TA, LA) and
three optical branches (ZO, TO, LO). ZA and ZO correspond
to an atomic motion perpendicular to the graphene plane (*z*
direction), all the other branches are polarized parallel to the
plane."

Being motivated by work I want to reproduce this curve. Please guide me.

Thanking you

Barnali Bhattacharya

CSIR SRF, Assam University,

Silchar-788011

Assam, INDIA


On Fri, Dec 1, 2017 at 12:03 AM, Lorenzo Paulatto <paulatz at gmail.com> wrote:

> Dear Barnali,
> There is no LO-TO splitting in graphene, or more precisely, it is zero.
>
> Kind regards
>
> --
> Lorenzo Paulatto
> Written on a virtual keyboard with real fingers
>
> On 30 Nov 2017 3:59 pm, "Barnali Bhattacharya" <barnalidgbhatt at gmail.com>
> wrote:
>
> Dear QE USERS,
>
>
>
> I am trying to reproduce the phonon dispersion with LO-TO splitting of graphene by using quantum espresso code.
>
> To get LO-TO splitting, I have added epsil=.true. as well as zeu=.true. in the input file of ph.x.  and calculated the phonon modes at q=0 (gamma point).
>
> Then I have used dynmat.x. for getting LO-TO splitting.
>
> At first, I did not added the propagation direction for q in the input file of dynmat.x .
>
>  After running dynmat.x, it gives the following line in the output
>
> ……………………………………………………..
>
> A direction for q was not specified:TO-LO splitting will be absent
>
> …………………………………………….
>
> Then I specify the q-point like
>
> q(1)=0.01, q(2)=0.0, q(3)=0.00 in the input file of dynmat.x .
>
> As a result the above line disappear from the output and the output is something like that
>
> …………………………………………………………………………………………………………………….
>
> Reading Dynamical Matrix from file dmat.gra
>
>      ...Force constants read
>
>      ...epsilon and Z* read
>
>      Acoustic Sum Rule: || Z*(ASR) - Z*(orig)|| =    2.089033E-02
>
>      Acoustic Sum Rule: ||dyn(ASR) - dyn(orig)||=    1.397683E-04
>
>
>
>      Polarizability (A^3 units)
>
>      multiply by 0.417318 for Clausius-Mossotti correction
>
>         25.389880    0.000000    0.000000
>
>          0.000000   25.389880    0.000000
>
>          0.000000    0.000000    1.110081
>
>
>
>      IR activities are in (D/A)^2/amu units
>
>
>
> # mode   [cm-1]    [THz]      IR
>
>     1     -0.00   -0.0000    0.0000
>
>     2     -0.00   -0.0000    0.0000
>
>     3     -0.00   -0.0000    0.0000
>
>     4    886.97   26.5907    0.0000
>
>     5   1701.94   51.0228    0.0000
>
>    6   1701.94   51.0228    0.0000
>
> ………………………………………………………………………………………………….
>
> So please tell me
>
> 1)  from which file LO-TO splitting can be found?
>
>
>
> 2) How can I get the phonon dispersion with LO-TO splitting of graphene?
>
>
>
>  I am waiting for any kind suggestions. For details, I am attaching here
> the input files and the dispersion curve which I want to reproduce?
>
>
>
> Thanks in advance.
>
>
>
> Sincerely
>
> Barnali Bhattacharya
>
> CSIR SRF, Assam University,
>
> Silchar-788011
>
> Assam, INDIA
>
>
>
>
>
>
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