[QE-users] I have failed to reproduce phonon dispersion of graphene

[Lorenzo Paulatto]

> Using a k-points grid that includes the K point can be a source of troubles, I would recommend using 16x16x1 or even 32x32x1 for better results.
p.s. and treat it as a metal, adding some smearing, to avoid the absurd dielectric constant

--
Lorenzo Paulatto - Paris
On Mar 30 2021, at 5:00 pm, Lorenzo Paulatto <paulatz at gmail.com> wrote:
> You have specified the q-points in crystal fractionary units, hence you have to specify q_in_cryst_coord=.true.
> This can be safely used in conjunction with q_in_band_form, which is a completely unrelated option.
>
> Also:
> You way of specifying the cell parameters is discouraged and may cause problems with symmetry detection, but it should work.
>
>
> > Using a k-points grid that includes the K point can be a source of troubles, I would recommend using 16x16x1 or even 32x32x1 for better results.
> hth
> --
> Lorenzo Paulatto - Paris
>
> On Mar 30 2021, at 4:19 pm, Evgenii <eisysoev4 at stud.eltech.ru> wrote:
> > Dear Quantum Espresso experts,
> >
> > I am having trouble calculating the phonon bands of graphene.
> >
> > First, I took the cif-file of the already relaxed graphite cell from the Materials Project site https://next-gen.materialsproject.org/ and made graphene cell from it by hand.
> > Then I relaxed the cell obtained with vc-relax and 12x12x1 k-point set.
> > I used the same parameters to perform a scf calculation:
> >
> > &CONTROL
> > calculation='scf'
> > title='graphene'
> > prefix='graphene'
> > verbosity='high'
> > restart_mode='from_scratch'
> > nstep=1000
> > iprint=1
> > tstress=.true.
> > tprnfor=.true.
> > disk_io='default'
> > pseudo_dir = '/home/mxm2/Desktop/Graphene',
> > outdir='/home/mxm2/Desktop/Graphene/temp'
> > /
> > &SYSTEM
> > ibrav = 0,
> > celldm(1)=1.889726,
> > nat = 2,
> > ntyp = 1,
> > ecutwfc = 60.0 ,
> > ecutrho = 480.0 ,
> > /
> > &ELECTRONS
> > electron_maxstep = 1000,
> > conv_thr = 1.0d-12 ,
> > mixing_mode = 'plain' ,
> > mixing_beta = 0.7d0 ,
> > /
> > ATOMIC_SPECIES
> > C 12.011 C.pz-rrkjus.UPF
> > ATOMIC_POSITIONS (crystal)
> > C 0.000000000 0.000000000 0.000861580
> > C 0.333333000 0.666667000 0.000838420
> > CELL_PARAMETERS (alat)
> > 2.438515837 -0.000000000 0.000000000
> > -1.219257919 2.111816662 0.000000000
> > -0.000000000 -0.000000000 19.995916314
> >
> > K_POINTS automatic
> > 12 12 1 0 0 0
> >
> > Then, I run ph.in calculation:
> >
> > &inputph
> > recover=.true.
> > tr2_ph=1.0d-14,
> > prefix='graphene',
> > ldisp=.true.
> > nq1=12,
> > nq2=12,
> > nq3=1,
> > amass(1)=12.011,
> > outdir='/home/mxm2/Desktop/Graphene/temp',
> > fildyn='graphene.dyn',
> > /
> >
> > My q2r:
> >
> > &input
> > fildyn='graphene.dyn',
> > zasr='simple',
> > flfrc='graphene.12x12x1.fc'
> > /
> >
> > Matdyn input:
> >
> > &input
> > asr='simple',
> > amass(1)=12.011,
> > flfrc='graphene.12x12x1.fc',
> > flfrq='graphene.disp.freq'
> > q_in_band_form=.true.,
> > /
> > 4 ! number of q-points
> > 0.000 0.000 0.000 10 ! gamma point
> > 0.500 0.000 0.000 10 ! M
> > 0.333 0.333 0.000 10 ! K
> > 0.000 0.000 0.000 1 ! gamma point
> >
> > Plotband:
> >
> > graphene.disp.freq
> > 0 1600
> > graphene.disp.freq.dat
> > graphene.disp.freq.ps
> > 0
> > 100 0
> >
> > Why the phonon dispersion does not match the pictures from the papers and for calculations with e.g. 18x18x1 k-point and nq-point sets the output file of graphene.dyn1 look like:
> >
> > Dielectric Tensor:
> >
> > ************************ 166.332153320312 0.000000000000
> > 166.332275390625************************ 0.000000000000
> > 0.000000000000 0.000000000000 1.116060253916
> >
> > Effective Charges E-U: Z_{alpha}{s,beta}
> >
> > atom # 1
> > -11117471.575740195811 -0.002632206306 0.000000000000
> > -0.002632205375-11117471.579664016142 0.000000000000
> > 0.000000000000 0.000000000000 -0.003734609171
> >
> > Also, what is the best way to set the lattice parameters, via Ibrav or CELL_PARAMETERS?
> >
> > Any help is appreciated.
> >
> > Best regards,
> > Evgeniy Sysoev.
> >
> >
> > _______________________________________________
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>

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