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

[Ramesh Kumar Kamadurai]

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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