[QE-users] Electron Phonon Calculation: tolerance limit for P

[Ramesh Kumar Kamadurai]

Dear Xavier
Thank you for the detailed information. Yes I have already used pseudo
potential from the PseudoDojo library and observed exactly what you have
described. After the VC-relax the verification the verification scf
calculation showed a completely different pressure tensor. I did
not increase the cut-off till 200 Ry as you suggested but stopped at 90 Ry.
Will give it a try with 200 Ry. Thanks. Regards
K Ramesh Kumar
Assistant Professor
GITAM, University
Vizag, India

On Thu, Oct 27, 2022 at 1:53 PM Ramesh Kumar Kamadurai <rkamadur at gitam.edu>
wrote:

> Dear users
> I am trying to calculate el-Ph coupling constant and other properties for
> a superconductor. The input file is attached. I am a bit stuck with
> VC-Relax calculation as the system is not able to stabilize at 0.0 kbar. I
> followed all the suggestions given in forum
> 1. Increased Cut-off to maximum
> 2. Tried USPP,NC, Mixed and currently running with PBE-Sol
> 3. Sequentially done 2 VC Relax calculation but i am not able to sort out
> the issue.
> &CONTROL
>     calculation   = "vc-relax"
>     etot_conv_thr =  4.00000e-05
>     forc_conv_thr =  1.00000e-04
>     max_seconds   =  1.72800e+05
>     nstep         = 100
>     outdir        = "/home/sjacobs/tmp/"
>     prefix        = "PDZ-VCRELAX"
>     pseudo_dir    = "C:\Users\RAMESH\.burai\.pseudopot"
>     tprnfor       = .TRUE.
>     tstress       = .TRUE.
>     verbosity     = "high"
> /
>
> &SYSTEM
>     a           =  6.36512e+00
>     degauss     =  7.34986e-03
>     ecutrho     =  6.40000e+02
>     ecutwfc     =  8.00000e+01
>     ibrav       = 2
>     nat         = 4
>     nosym       = .FALSE.
>     nspin       = 1
>     ntyp        = 3
>     occupations = "smearing"
>     smearing    = "marzari-vanderbilt"
> /
>
> &ELECTRONS
>     conv_thr         =  8.00000e-10
>     electron_maxstep = 80
>     mixing_beta      =  4.00000e-01
>     startingpot      = "atomic"
>     startingwfc      = "atomic+random"
> /
>
> &IONS
>     ion_dynamics = "bfgs"
> /
>
> &CELL
>     cell_dofree    = "all"
>     cell_dynamics  = "bfgs"
>     press          =  0.00000e+00
>     press_conv_thr =  5.00000e-01
> /
>
> K_POINTS {automatic}
> 12 12 12  0 0 0
>
> ATOMIC_SPECIES
> Ga     69.72300  Ga.pbesol-dnl-rrkjus_psl.1.0.0.UPF
> Pd    106.42000  Pd_ONCV_PBEsol-1.0.upf
> Zr     91.22400  zr_pbesol_v1.uspp.F.UPF
>
> ATOMIC_POSITIONS {crystal}
> Zr      0.000000   0.000000   0.000000
> Ga      0.493162   0.493162   0.493162
> Pd      0.739743   0.739743   0.739743
> Pd      0.246581   0.246581   0.246581
>
> The output stress is given below
> entering subroutine stress ...
>           total   stress  (Ry/bohr**3)                   (kbar)     P=
>  2.67
>      entering subroutine stress ...
>           total   stress  (Ry/bohr**3)                   (kbar)     P=
> -0.41
>      entering subroutine stress ...
>           total   stress  (Ry/bohr**3)                   (kbar)     P=
> -0.82
>      entering subroutine stress ...
>           total   stress  (Ry/bohr**3)                   (kbar)     P=
>  0.56
>      entering subroutine stress ...
>           total   stress  (Ry/bohr**3)                   (kbar)     P=
>  0.13
>      entering subroutine stress ...
>           total   stress  (Ry/bohr**3)                   (kbar)     P=
> -0.08
>      entering subroutine stress ...
>           total   stress  (Ry/bohr**3)                   (kbar)     P=
> -0.23
>      entering subroutine stress ...
>           total   stress  (Ry/bohr**3)                   (kbar)     P=
> -0.35
>      entering subroutine stress ...
>           total   stress  (Ry/bohr**3)                   (kbar)     P=
> -0.50
>      entering subroutine stress ...
>           total   stress  (Ry/bohr**3)                   (kbar)     P=
> -0.63
>      entering subroutine stress ...
>           total   stress  (Ry/bohr**3)                   (kbar)     P=
> -0.77
>      entering subroutine stress ...
>           total   stress  (Ry/bohr**3)                   (kbar)     P=
> -0.83
> My question is
> What is the optimal pressure value to avoid negative frequencies for
> electron phonon calculation ?
> Is there any mistake in my input file ?
> Thanks in advance
> Regards
> Ramesh
> Asst. Professor
> GITAM University
> Vizag, India
>
>
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