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

Fri, 04 Aug 2023 07:15:13 -0700

Try CRYSTAL 23 or vesta 

On Fri, 4 Aug 2023 at 16:23, Giuseppe Scala <g.sca...@campus.unimib.it> wrote:
I used a YouTube tutorial with BURAI for creating this input file, sigh. What should I do to create a right Bilayer using Burai or another software? 

Il ven 4 ago 2023, 12:14 ANAND JHA <anandk...@iitk.ac.in> ha scritto:
Its wrong 
Becauese vaccume will be after the top surface of bilayer so u need to add vaccume on your top bilayer 

On Fri, 4 Aug 2023 at 15:38, Giuseppe Scala <g.sca...@campus.unimib.it> wrote:
The c parameter is set in that way in order to have 10 angstrom vacuum between two sets of Bilayer in my structure. If I reduce the c parameter i think that my system won't be a Bilayer anymore. Is that line of reasoning wrong?

Il ven 4 ago 2023, 05:15 ANAND JHA <anandk...@iitk.ac.in> ha scritto:
C parameter and a parameter are wrong they are too high and low

On Thu, 3 Aug 2023 at 20:01, Giuseppe Scala <g.sca...@campus.unimib.it> wrote:
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 <anandk...@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.sca...@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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