[Pw_forum] Phonon dispersion with LO-TO splitting

[Lorenzo Paulatto]

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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