[Pw_forum] convergence for CaMg2

[adwait mevada]

Dear All,
I am trying to find optimal ecutwfc for CaMg2.
As a first step i varied ecutwfc from 30-150 but i found that
energy was fluctuating
I cannot decide what to set for ecutrho if my ecutwfc is fluctuating
, what can be the reason for this? any help in this regard is appreciated.

note : i am not finding ecutwfc for equilibrium volume.

I am attaching png output of gnuplot for it.

data for various ecutwfc
ecut    energy                 vol              kpoints  stress  time.

30     -932.78387473      1314.9516     40   459.00   7m 4.75s
40     -932.78292968      1314.9516     40   458.52  10m35.69s
50     -932.78368793      1314.9516     40   458.74  14m22.97s
60     -932.78388413      1314.9516     40   458.90  17m48.05s
70     -932.78547210      1314.9516     40   457.91  25m37.98s
80     -932.78563717      1314.9516     40   459.77  29m17.84s
90     -932.78419457      1314.9516     40   459.42  35m28.98s
100     -932.78387315      1314.9516     40   458.78  37m40.76s
110     -932.78425940      1314.9516     40   458.38  41m34.44s
120     -932.78459959      1314.9516     40   458.94  52m35.88s
130     -932.78422725      1314.9516     72   459.24      2h 0m
140     -932.78394222      1314.9516     72   458.91      2h 3m
150     -932.78396419      1314.9516     72   458.69      2h30m
my input file is:
C=9
A=5
for ECUT in 30 40 50 60 70 80 90 100 ; do
cat > camg2e$ECUT.in << EOF
 &control
    calculation = 'scf'
    prefix='camg2e$ECUT',
    tstress = .true.
    tprnfor = .true.
 /
 &system
    ibrav=4, a=$A ,c=$C ,nat=12, ntyp=2,
    ecutwfc=$ECUT ! ,ecutrho=480,
    occupations='smearing',smearing="mv",degauss=0.02,
 /
 &electrons
    diagonalization='david'
    mixing_mode = 'plain'
    mixing_beta = 0.7
    conv_thr =  1.0d-8
 /
ATOMIC_SPECIES
 Mg  24.305  Mg.pw91-np-van.UPF
 Ca  40.078  Ca.pw91-nsp-van.UPF
ATOMIC_POSITIONS crystal
Ca      0.3333333   0.6666667   0.0668052
Ca      0.3333333   0.6666667   0.4331948
Ca      0.6666667   0.3333333   0.5668053
Ca      0.6666667   0.3333333   0.9331947
Mg      0.0000000   0.0000000   0.0000000
Mg      0.0000000   0.0000000   0.5000000
Mg      0.3397683   0.1698842   0.2500000
Mg      0.8301158   0.6602317   0.2500000
Mg      0.1698842   0.8301158   0.7500000
Mg      0.8301158   0.1698842   0.2500000
Mg      0.1698842   0.3397683   0.7500000
Mg      0.6602317   0.8301158   0.7500000
K_POINTS automatic
8 8 4 1 1 1
EOF
mpirun -np 4   pw.x -in camg2e$ECUT.in > camg2e$ECUT.out
   ENERGY=`grep ! camg2e$ECUT.out | cut -b 33-49`
   VOL=`grep volume camg2e$ECUT.out | cut -b 33-45 `
   KP=`grep points= camg2e$ECUT.out | cut -b 25-31`
   TIME=`grep "PWSCF  " camg2e$ECUT.out | cut -b 37-47`
   STRESS=`grep "total   stress" camg2e$ECUT.out | cut -b 72-78`
   FOR=`grep "Total force  " camg2e$ECUT.out`
   echo "$ECUT $ENERGY $ALAT $VOL $KP $STRESS $TIME $FOR"
sleep 60
   echo "$ECUT $ENERGY $ALAT $VOL $KP $STRESS $TIME $FOR" >> camg2r480.dat
done

Thank you for your help in advance

-- 
-Adwait
Ph.D. Student,
Gujarat University,
Gujarat, India.
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