[Pw_forum] convergence for CaMg2

[Giovanni Cantele]

one of the problems that you might be running across is that you keep ecutrho fixed. That means that with ecutwfc=30, ecutrho/ecutwfc=16, whereas with ecutwfc=120, the same ratio is 4. The latter is definitely too small for ultrasoft pseudo potentials, that you are including in your calculation. In other words, you might be comparing values of the total energies with different convergence levels with respect to ecutrho, which can be the origin (or a partial explanation) of the oscillations you find.

I would try (maybe this will not solve your problem!) to retry the test as a function of ecutwfc, as you did, but keeping the ecutrho/ecutwfc ratio (rather than the ecutrho variable) constant, to a more or less safe value (e.g. 8).

Giovanni

> On 23 Oct 2015, at 17:05, adwait mevada <adwait.mevada at gmail.com> wrote:
> 
> 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.
> <camg2ecut.png>_______________________________________________
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-- 

Giovanni Cantele, PhD
CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: giovanni.cantele at spin.cnr.it
Phone: +39 081 676910
Skype contact: giocan74

ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: http://people.na.infn.it/~cantele