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

[Lorenzo Paulatto]

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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