[Pw_forum] What is the exact criteria for scf convergence?

[Emine Kucukbenli]

Hi M,  The parameter in play here is called "upscale", take a look at the
description of it in input parameters list. (Also for big systems one might
want to keep in mind that conv_thr is an extensive quantity) cheers - emine


On Sat, Feb 7, 2015 at 3:11 PM, MKondrin <mkondrin at hppi.troitsk.ru> wrote:

> Hello!
>
> I try to optimize quite large structure (several tens of atoms in the
> unit cell) but I can not quite get that is the criteria of convergence
> to proceed for the next optimization cycle. I use QE 5.01
>
> I have in the preamble of input file something like:
>
> &control
> calculation='relax',
> prefix='scf',
> tstress=.true.,
> tprnfor=.true.,
> pseudo_dir = '../pseudo',
> outdir='./tmp'
> /
> &system
> ibrav=0,
> celldm(1) = 12.60447,
> ntyp=2,
> nat=84,
> ecutwfc=70,
> ecutrho=800,
> occupations='fixed'
> /
> &electrons
>     mixing_beta = 0.7,
>     conv_thr =  1.0d-6
> /
> &ions
> /
> ....
>
> I suppose that the next cycle of structure optimization should occur
> than the accuracy of self consistent calculations of about 1e-6 Ry.
>
> However in the output file I get this (this is the end of one scf cycle)
>
>      iteration # 20     ecut=    70.00 Ry     beta=0.70
>      Davidson diagonalization with overlap
>      ethr =  5.68E-10,  avg # of iterations =  1.0
>
>      total cpu time spent up to now is   230665.4 secs
>
>      total energy              =    -823.97008715 Ry
>      Harris-Foulkes estimate   =    -823.97008883 Ry
>      estimated scf accuracy    <       0.00000279 Ry
>
>      iteration # 21     ecut=    70.00 Ry     beta=0.70
>      Davidson diagonalization with overlap
>      ethr =  5.68E-10,  avg # of iterations =  4.0
>
>      total cpu time spent up to now is   233303.9 secs
>
>      total energy              =    -823.97008869 Ry
>      Harris-Foulkes estimate   =    -823.97008855 Ry
>      estimated scf accuracy    <       0.00000071 Ry
>
>      iteration # 22     ecut=    70.00 Ry     beta=0.70
>      Davidson diagonalization with overlap
>      ethr =  3.37E-10,  avg # of iterations =  1.0
>
>      total cpu time spent up to now is   236012.3 secs
>
>      total energy              =    -823.97008898 Ry
>      Harris-Foulkes estimate   =    -823.97008869 Ry
>      estimated scf accuracy    <       0.00000092 Ry
>
>      iteration # 23     ecut=    70.00 Ry     beta=0.70
>      Davidson diagonalization with overlap
>      ethr =  3.37E-10,  avg # of iterations =  3.5
>
>      total cpu time spent up to now is   238645.5 secs
>
>      total energy              =    -823.97008880 Ry
>      Harris-Foulkes estimate   =    -823.97008904 Ry
>      estimated scf accuracy    <       0.00000178 Ry
>
>      iteration # 24     ecut=    70.00 Ry     beta=0.70
>      Davidson diagonalization with overlap
>      ethr =  3.37E-10,  avg # of iterations =  1.0
>
>      total cpu time spent up to now is   241385.7 secs
>
>      total energy              =    -823.97008829 Ry
>      Harris-Foulkes estimate   =    -823.97008881 Ry
>      estimated scf accuracy    <       0.00000147 Ry
>
>      iteration # 25     ecut=    70.00 Ry     beta=0.70
>      Davidson diagonalization with overlap
>      ethr =  3.37E-10,  avg # of iterations =  3.9
>
>      total cpu time spent up to now is   244038.6 secs
>
>      total energy              =    -823.97008797 Ry
>      Harris-Foulkes estimate   =    -823.97008835 Ry
>      estimated scf accuracy    <       0.00000057 Ry
>
>      iteration # 26     ecut=    70.00 Ry     beta=0.70
>      Davidson diagonalization with overlap
>      ethr =  2.72E-10,  avg # of iterations =  4.0
>
>      total cpu time spent up to now is   246730.6 secs
>
>      total energy              =    -823.97008832 Ry
>      Harris-Foulkes estimate   =    -823.97008847 Ry
>      estimated scf accuracy    <       0.00000043 Ry
>
>      iteration # 27     ecut=    70.00 Ry     beta=0.70
>      Davidson diagonalization with overlap
>      ethr =  2.03E-10,  avg # of iterations =  1.0
>
>      total cpu time spent up to now is   249273.6 secs
>
>      total energy              =    -823.97008831 Ry
>      Harris-Foulkes estimate   =    -823.97008833 Ry
>      estimated scf accuracy    <       0.00000021 Ry
>
>      iteration # 28     ecut=    70.00 Ry     beta=0.70
>      Davidson diagonalization with overlap
>      ethr =  9.87E-11,  avg # of iterations =  1.1
>
>      total cpu time spent up to now is   252028.1 secs
>
>      total energy              =    -823.97008826 Ry
>      Harris-Foulkes estimate   =    -823.97008832 Ry
>      estimated scf accuracy    <       0.00000017 Ry
>
>      iteration # 29     ecut=    70.00 Ry     beta=0.70
>      Davidson diagonalization with overlap
>      ethr =  8.33E-11,  avg # of iterations =  6.2
>
>      total cpu time spent up to now is   254596.4 secs
>
>      End of self-consistent calculation
>
>
> Aren't the cycles after #25 superfluous, because energy difference
> between two successive steps and estimated accuracy is less than 1e-6
> Ry? What is the control parameter that help me to reduce the number of
> steps ?
>
> Thank you in advance!
>
> M. V. Kondrin (High Pressure Physics Institute RAS, Troitsk, Russia)
>
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