[Pw_forum] slab relaxtion in external field can't reach convergence

Liping YU lyu7 at ncsu.edu
Sat Nov 19 05:29:01 CET 2005


Dear PWSCF users,

I am trying to use pw.x (version 2.1.5) relax a slab in a fixed external 
electric field.  I do this by setting following variables in the input 
file for 'relax' calculation.
 >> tefield = .true.,    edir = 3,    eamp = 0.02,    emaxpos = 0.00,  
eopreg = 0.01<<
(note: the slab is centered in the middle of the supercell and 
(thickness) occupies 3/5 in z-direction.)

My problem is that:  the program always finishes running after < 5 bfgs 
steps without any convergences (the atom positions didn't change and 
forces on them were still very large). But if I set 'eamp=0.0' and leave 
all other variables unchanged in the same input file(which is the case I 
think for applying zero field) , it works well and structure is relaxed 
to where I want. Do you have any idea on this?  Many thanks in advance!

liping
----------------------------
my input file:
----------------------------
 &CONTROL
                       title = 'relax TiO2 terminated [001] te-PbTiO3 
slab 7layers+4vacs' ,
                 calculation = 'relax' ,
                restart_mode = 'from_scratch' ,
                      outdir = './tmp/' ,
                  pseudo_dir = '../../pseudo/' ,
                      prefix = 'te-pb.slab' ,
               etot_conv_thr = 1.0D-4,
               forc_conv_thr = 5.0D-4,
                       nstep = 250,
                     tstress = .true. ,
                     tprnfor = .true. ,
                     tefield = .true. ,
                          dt = 120 ,
 /
 &SYSTEM
            ibrav = 6,
        celldm(1) = 7.284856,
        celldm(3) = 5.2010,
              nat = 18,
             ntyp = 3,
      occupations = 'smearing',
         smearing = 'gaussian',
          degauss = 0.01,
          ecutwfc = 30.0,
          ecutrho = 250.0,
             edir = 3,
          emaxpos = 0.00,
           eopreg = 0.01,
             eamp = 0.01,
            nosym = .true.
 /
 &ELECTRONS
 electron_maxstep = 100,
  diagonalization = 'cg' ,
      mixing_beta = 0.1,
         conv_thr = 1.D-8,
 /
 &IONS
    upscale=10.d0
 /
ATOMIC_SPECIES
    Pb  207.2000   Pb.pz-d-van.UPF
    Ti  47.86700   022-Ti-ca-sp-vgrp.uspp.UPF
    O   16.00000   008-O-ca--vgrp.uspp.UPF
ATOMIC_POSITIONS crystal
O    0.5   0.0   0.78039   0 0 1
O    0.0   0.5   0.78039   0 0 1
Ti   0.5   0.5   0.79368   0 0 1
O    0.5   0.5   0.68299   0 0 1
Pb   0.0   0.0   0.70000   0 0 1
O    0.5   0.0   0.58039   0 0 1
O    0.0   0.5   0.58039   0 0 1
Ti   0.5   0.5   0.59368   0 0 1
O    0.5   0.5   0.48299   0 0 1
Pb   0.0   0.0   0.50000   0 0 0
O    0.5   0.0   0.38039   0 0 1
O    0.0   0.5   0.38039   0 0 1
Ti   0.5   0.5   0.39368   0 0 1
O    0.5   0.5   0.28299   0 0 1
Pb   0.0   0.0   0.30000   0 0 1
O    0.5   0.0   0.18039   0 0 1
O    0.0   0.5   0.18039   0 0 1
Ti   0.5   0.5   0.19368   0 0 1
K_POINTS automatic
5 5 1 0 0 0
------------------
part of output
-------------------
!    total energy              = -1180.25248656 ryd
     estimated scf accuracy    <        4.3E-09 ryd

     band energy sum           =   -99.32162764 ryd
     one-electron contribution = -3491.94140692 ryd
     hartree contribution      =  1812.19849675 ryd
     xc contribution           =  -176.79463848 ryd
     ewald contribution        =   674.50015201 ryd
     electric field correction =     1.79085470 ryd
     correction for metals     =    -0.00594461 ryd

     convergence has been achieved

     Forces acting on atoms (Ry/au):

     atom   1 type  3   force =     0.00000000    0.00000000   -0.00637085
     atom   2 type  3   force =     0.00000000    0.00000000   -0.00637069
     atom   3 type  2   force =     0.00000000    0.00000000   -0.06007066
     atom   4 type  3   force =     0.00000000    0.00000000    0.01979378
     atom   5 type  1   force =     0.00000000    0.00000000    0.09385845
     atom   6 type  3   force =     0.00000000    0.00000000   -0.03255876
     atom   7 type  3   force =     0.00000000    0.00000000   -0.03255858
     atom   8 type  2   force =     0.00000000    0.00000000    0.00631018
     atom   9 type  3   force =     0.00000000    0.00000000   -0.00570834
     atom  10 type  1   force =     0.00000000    0.00000000    0.07250243
     atom  11 type  3   force =     0.00000000    0.00000000   -0.03060398
     atom  12 type  3   force =     0.00000000    0.00000000   -0.03060406
     atom  13 type  2   force =     0.00000000    0.00000000    0.01326980
     atom  14 type  3   force =     0.00000000    0.00000000   -0.02455655
     atom  15 type  1   force =     0.00000000    0.00000000    0.05976386
     atom  16 type  3   force =     0.00000000    0.00000000   -0.04895601
     atom  17 type  3   force =     0.00000000    0.00000000   -0.04895608
     atom  18 type  2   force =     0.00000000   -0.00000001    0.06181605

     Total force =     0.172980     Total SCF correction =     0.000128

     number of scf cycles    =   4
     number of bfgs steps    =   1

     energy old              =   -1182.1383466357 ryd
     energy new              =   -1180.2524865583 ryd

     CASE: energy_new > energy_old

     new trust radius        =       0.0000000000 bohr


     bfgs converged in   4 scf cycles and   1 bfgs steps

     End of BFGS geometry calculation

     Final energy            =   -1182.1383466357 ryd

     Saving the approximate inverse hessian


CELL_PARAMETERS (alat)
   1.000000000   0.000000000   0.000000000
   0.000000000   1.000000000   0.000000000
   0.000000000   0.000000000   5.201000000

ATOMIC_POSITIONS (crystal)
O        0.500000000   0.000000000   0.780390000
O        0.000000000   0.500000000   0.780390000
Ti       0.500000000   0.500000000   0.793680000
O        0.500000000   0.500000000   0.682990000
Pb       0.000000000   0.000000000   0.700000000
O        0.500000000   0.000000000   0.580390000
O        0.000000000   0.500000000   0.580390000
Ti       0.500000000   0.500000000   0.593680000
O        0.500000000   0.500000000   0.482990000
Pb       0.000000000   0.000000000   0.500000000
O        0.500000000   0.000000000   0.380390000
O        0.000000000   0.500000000   0.380390000
Ti       0.500000000   0.500000000   0.393680000
O        0.500000000   0.500000000   0.282990000
Pb       0.000000000   0.000000000   0.300000000
O        0.500000000   0.000000000   0.180390000
O        0.000000000   0.500000000   0.180390000
Ti       0.500000000   0.500000000   0.193680000



     Writing file te-pb.slab.sav for program phonon

     PWSCF        :     1h 7m CPU time




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