[QE-users] Negative frequencies for phonon dispersion in Bilayer MoS2

[Giuseppe Scala]

Hi ANAND,

Would you mind if I ask you to tell me where's the problem in the
structure? Maybe that c parameter is too high or low?
Il gio 3 ago 2023, 12:58 ANAND JHA <anandkj21 at iitk.ac.in> ha scritto:

> There is some issue in your bilayer
> Try to make a new bilayer with CRYSTAL SOFTWARE
>
> On Thu, 3 Aug 2023 at 03:55, Giuseppe Scala <g.scala2 at campus.unimib.it>
> wrote:
>
>> I get negative frequencies at gamma points for Bilayer MoS2. I relaxed my
>> structure and checked convergence with respect to energy cutoff. That's my
>> input file for the scf calculation:
>>
>> ##############
>>
>> &CONTROL
>> calculation ='scf'
>> prefix = 'MoS2_BI'
>> pseudo_dir = '/home/Giuseppe'
>> outdir = './'
>> tstress = .true.
>> tprnfor = .true.
>> forc_conv_thr = 1.0d-3
>> nstep = 200
>> /
>>
>>      &SYSTEM
>> ibrav = 4
>> a = 3.1429635960300000000
>> c = 20.006663000000000000
>> nat = 6
>> ntyp = 2
>> ecutwfc = 60
>> ecutrho = 240
>> occupations = 'smearing'
>> degauss = 0.01
>> /
>>
>>     &ELECTRONS
>> mixing_beta = 0.7
>> conv_thr = 1.0d-8
>> diagonalization = 'david'
>> electron_maxstep=200
>> /
>>
>>     &IONS
>> trust_radius_max = 0.2
>> /
>>     &CELL
>> cell_dynamics = "bfgs"
>> cell_dofree = '2Dxy'
>> /
>>
>> ATOMIC_SPECIES
>> Mo 95.9400 Mo.pbesol-spn-kjpaw_psl.1.0.0.UPF
>> S 32.0660 S.pbesol-n-kjpaw_psl.1.0.0.UPF
>> ATOMIC_POSITIONS {angstrom}
>> Mo 1.5714815237 0.9072955423 6.6890512735
>> Mo 0.0000000000 1.8145901001 13.377562735
>>  S 1.5714815237 0.9072955423 11.825385701
>>  S 1.5714815237 0.9072955423 14.928508325
>>  S 0.0000000000 1.8145901001 8.2412092563
>>  S 0.0000000000 1.8145901001 5.1381015776
>>
>> K_POINTS {automatic}
>> 4 4 4 0 0 0
>>
>> #########
>>
>>
>> And here my input file for ph.x
>>
>>
>> #######
>>
>> &inputph
>> prefix = 'MoS2_BI'
>> fildvscf = 'dvscf'
>> ldisp = .true.
>> fildyn = 'MoS2_BI.dyn'
>> alpha_mix(1) = 0.3
>> nq1 = 2,
>> nq2 = 2,
>> nq3 = 2,
>> tr2_ph = 1.0d-12
>> /
>> ########
>>
>> Is my bilayer wrong? I've come the exact same calculations for Bulk and
>> Monolayer MoS2 and everything went smoothly
>>
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>
> _______________________________________________
> The Quantum ESPRESSO community stands by the Ukrainian
> people and expresses its concerns about the devastating
> effects that the Russian military offensive has on their
> country and on the free and peaceful scientific, cultural,
> and economic cooperation amongst peoples
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users
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