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

[Cignarella Chiara]

Dear Giuseppe,

Can you include also the output files?

Did you apply the acoustic sun rules with matdyn.x (or dynmat)?

Best

Chiara Cignarella
PhD student
THEOS, EPFL Lausanne

> On 3 Aug 2023, at 00:26, 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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