[Pw_forum] Question about the error during bond distance energy scan

[JeJoon Yeon]

Hello

I tried to calculate the potential energies of systems with Cu (100) and a
thiol molecule (SCH3). Here, SCH3 is placed on the center hole of the Cu
(100) surface. I tried to "lift" and "push" the thiol from the optimal
position by every 0.2 angstrom in z-dir. In other words, I tried to fix the
Cu-S bond distances every 0.2A step in z-dir, and calculated the energies
of each step. I used 4 processors per each calculation. I optimized the
ecut values using scf calculations before those relaxation calculations.

However, the calculations all failed with errors:
a) Error in routine checkallsym (1): some of the original symmetry
operations not satisfied
b) Error in routine check_constraint (1): on some constraint g = 0 is not
satisfied
Either a or b, all of my calculations failed.

I tried
1) increased k-point to 8 8 1
2) increased / decreased 2 of ecut values
3) different pseudopotentials - pbe-van series
But all failed.

What should I need to fix, to perform such bond distance scan? Especially,
I feel the calculations are more unstable when I calculate the too close
distance and dissociated state. Please let me know what options should be
modified.

Following is a part of my script to calculate the energy of systems.

for i in 1.94727 2.01802 2.10546 2.20761 2.32252 2.44840 2.58364 2.72686
2.88042 3.03264 3.19334 3.35827 3.52683 3.69853 3.87294 4.04641; do
cupos=5.559607271
SCdis=1.847269479
CHdis=0.350112275
spos=`bc <<< "$i+$cupos"`
cpos=`bc <<< "$i+$cupos+$SCdis"`
hpos=`bc <<< "$i+$cupos+$SCdis+$CHdis"`
TMP_DIR=$INPUT_DIR/tmp_$i
mkdir -p $TMP_DIR

cat > ${INPUT}_${i}.in << EOF
&CONTROL
  prefix="${INPUT}_${i}",
  calculation='relax',
  outdir="$TMP_DIR",
  pseudo_dir="$PSEUDO_DIR",
  restart_mode= 'from_scratch',
  nstep = 200,
/

&SYSTEM
  ibrav=0,
  nat=21,
  ntyp=4,
  ecutwfc=75,
  ecutrho=580,
  occupations='smearing',
  smearing='methfessel-paxton',
  degauss=0.05,
/

&ELECTRONS
  diagonalization='david',
  conv_thr=1d-07,
  mixing_mode='plain',
  mixing_beta=0.100,
/

&IONS
  ion_dynamics = "damp",
/

ATOMIC_SPECIES
  Cu 63.546000 Cu.pbe-dn-rrkjus_psl.0.2.UPF
  S 32.065 S.pbe-n-rrkjus_psl.0.1.UPF
  C 12.010700 C.pbe-n-rrkjus_psl.0.1.UPF
  H 1.00794 H.pbe-rrkjus_psl.0.1.UPF

ATOMIC_POSITIONS {angstrom}
Cu       1.277917324   1.277917324   1.986989651
Cu       1.277924773   3.834096475   1.968243141
Cu       3.834096475   1.277924773   1.968243141
Cu       3.834152049   3.834152049   1.964836906
Cu      -0.007650369  -0.007650369   3.757264137
Cu      -0.007713787   2.563076890   3.757098988
Cu       2.563076890  -0.007713787   3.757098988
Cu       2.563146875   2.563146875   3.756943186
Cu       1.277643630   1.277643630   5.559607271
Cu       1.277264882   3.832919091   5.603109167
Cu       3.832919091   1.277264882   5.603109167
Cu       3.832950472   3.832950472   5.660547118
Cu      -0.032137093  -0.032137093   7.445476752
Cu      -0.033221407   2.585994776   7.447578702
Cu       2.585994776  -0.033221407   7.447578702
Cu       2.587199888   2.587199888   7.449822416
S        1.279623674   1.279623674   $spos
C        1.280325150   1.280325150   $cpos
H        0.546327157   0.546327157   $hpos
H        2.282789775   1.011689776   $hpos
H        1.011689776   2.282789775   $hpos

K_POINTS {automatic}
  4 4 1 0 0 0

CELL_PARAMETERS {angstrom}
   5.112330000   0.000000000   0.000000000
   0.000000000   5.112330000   0.000000000
   0.000000000   0.000000000   20.00000000

CONSTRAINTS
4 0.01
distance 13 17 $i
distance 14 17 $i
distance 15 17 $i
distance 16 17 $i
EOF

Thank you

Best wishes

Joon
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