[Pw_forum] Convergence issue for C/BN slab

[Namita Narendra]

Hi,

I am trying to relax a (111) diamond/cubic-BN slab and the total force on
the atom is not converging. Initially, the scf cycle itself was not
converging and I needed to introduce smearing with degauss=0.01 to achieve
scf convergence. Now, the relaxation is not converging and the total force
on the atom is oscillating. I have tried mixing of 'local-TF', reduced
mixing_beta, used damped ion dynamics and tried LDA pseudopotential. None
of this has helped with the convergence issue. Attached below is the input
file used.

 &CONTROL
calculation = 'relax' ,
restart_mode = 'from_scratch' ,
wf_collect = .true. ,
outdir = '/share2/nnarend/espresso/c_bn1' ,
pseudo_dir = '/home/nnarend/pseudo' ,
prefix = 'C_BN_1' ,
tstress = .true. ,
tprnfor = .true. ,
       forc_conv_thr=1.0D-3,
       etot_conv_thr=1.0D-4
 /
 &SYSTEM
ibrav = 8,
celldm(1) = 8.291523,
       celldm(2)=0.57735,
       celldm(3)=6,
       nat = 24,
ntyp = 3,
ecutwfc=180.0,
       occupations='smearing',
       smearing='cold',
       degauss=0.01

 /
 &ELECTRONS
conv_thr = 1.0d-8,
mixing_mode = 'plain' ,
mixing_beta = 0.3 ,
diagonalization = 'david' ,
 /
 &IONS
 /
ATOMIC_SPECIES
   B  10.811  B.pbe-nc.UPF
   N  14.007  N.pbe-nc.UPF
   C  12.011 C.pbe-nc.UPF

ATOMIC_POSITIONS alat
C 0.000000   0.000000   0.000000
C 0.500000   0.288675   0.000000
C 0.166667   0.288675   0.117851
C 0.666667   0.000000   0.117851
C 0.166667   0.288675   0.471404
C 0.666667   0.000000   0.471404
C 0.333333   0.000000   0.589255
C 0.833333   0.288675   0.589255
C 0.333333   0.000000   0.942808
C 0.833333   0.288675   0.942808
C 0.000000   0.000000   1.060659
C 0.500000   0.288675   1.060659
B 0.000000   0.000000   1.414212
B 0.500000   0.288675   1.414212
N 0.166667   0.288675   1.532063
N 0.666667   0.000000   1.532063
B 0.166667   0.288675   1.885616
B 0.666667   0.000000   1.885616
N 0.333333   0.000000   2.003467
N 0.833333   0.288675   2.003467
B 0.333333   0.000000   2.357020
B 0.833333   0.288675   2.357020
N 0.000000   0.000000   2.474871
N 0.500000   0.288675   2.474871

K_POINTS automatic
8 8 6 0 0 0

Below is the force at the end of each bfgs cycle

     Total force =     0.492043     Total SCF correction =     0.000193
     Total force =     0.170844     Total SCF correction =     0.000253
     Total force =     0.049967     Total SCF correction =     0.000085
     Total force =     0.038773     Total SCF correction =     0.000075
     Total force =     0.042155     Total SCF correction =     0.000056
     Total force =     0.046807     Total SCF correction =     0.000072
     Total force =     0.044401     Total SCF correction =     0.000064
     Total force =     0.034652     Total SCF correction =     0.000095
     Total force =     0.033861     Total SCF correction =     0.000065
     Total force =     0.107334     Total SCF correction =     0.000129
     Total force =     0.071144     Total SCF correction =     0.000057
     Total force =     0.053109     Total SCF correction =     0.000077
     Total force =     0.058897     Total SCF correction =     0.000087
     Total force =     0.075144     Total SCF correction =     0.000061
     Total force =     0.109071     Total SCF correction =     0.000025
     Total force =     0.121561     Total SCF correction =     0.000042
     Total force =     0.128205     Total SCF correction =     0.000048
     Total force =     0.138713     Total SCF correction =     0.000070

Thanks,
Namita
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