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

[mkondrin]

Dear Ramesh,

It seems to me that some small negative values in phonon calculations is 
unavoidable. They occur rather sporadically (especially for acoustic 
modes in Gamma point) and the best way to deal with them is just ignore 
them. For electron-phonon calculations it is better not to use lambda.x 
program (it does not tolerate negative frequencies) but follow the way 
described in this thread -- 
https://lists.quantum-espresso.org/pipermail/users/2022-September/049463.html

Sincerely yours,
M.V. Kondrin

On 10/27/2022 11:23 AM, Ramesh Kumar Kamadurai via users 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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