[Pw_forum] Phonon dispersion with LO-TO splitting

[Lorenzo Paulatto]

There is no LO-TO splitting in that paper, nor in the figure you've sent.
LO-TO splitting is a very specific effect that happens at Gamma: At Gamma
the LO and TO bands of graphene are degenerate.

You can find an explanation of LO-TO splitting in any solid state book and
a gazillion web sites, in any language. Have a look around, then please
come back to the forum if you have some specific question.

Kind regards


-- 
Lorenzo Paulatto
Written on a virtual keyboard with real fingers

On 4 Dec 2017 1:33 pm, "Barnali Bhattacharya" <barnalidgbhatt at gmail.com>
wrote:

> 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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