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" <[email protected]> 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 <[email protected]> > 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" <[email protected]> >> 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 >> >> >> >> >> >> >> _______________________________________________ >> Pw_forum mailing list >> [email protected] >> http://pwscf.org/mailman/listinfo/pw_forum >> >> >> >> _______________________________________________ >> Pw_forum mailing list >> [email protected] >> http://pwscf.org/mailman/listinfo/pw_forum >> > > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum >
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