[Pw_forum] conversence problem in vc-relax (Atom Mass in relaxation)
Sandro Scandolo
scandolo at ictp.it
Mon Sep 10 22:23:14 CEST 2007
Dear Yukihiro,
while a higher accuracy may be required in some exceptional cases,
converging the stress tensor (or the average pressure) within 1 kbar of
the target value is already a physically sound achievement. The error
DeltaV in volume that one is making with a DeltaP~+-1 kbar error in the
pressure is given by DeltaV/V=DeltaP/Bulk_modulus. With the exception of
molecular or very soft solids, the bulk modulus of the vast majority of
solids is typically > 10 GPa, or 100 kbar, so your volume is likely to
be converged to better than 1% already....
This of course should not prevent you from asking a higher accuracy, if
required, in which case Cesar's comments are likely to be helpful.
Regards,
Sandro
Yukihiro Okuno wrote:
> Dear PWScf Users.
>
> I'm Yukihiro Okuno.
>
> I had posted about the Atom Mass in vc-relax, and thank you for the responces.
> We set same atom mass 20.0 ( average of atom mass), and do vc-relax calculation as
> the following input file,
>
>
> &control
> calculation = 'vc-relax',
> restart_mode = 'from_scratch',
> pseudo_dir = '/pseudo/',
> outdir = './',
> prefix='vc-test'
> nstep = 100
> etot_conv_thr = 1.0D-5
> forc_conv_thr = 1.0D-4
> dt = 80.0
> tstress = .true.
> tprnfor = .true.
> /
> &system
> ibrav=6
> celldm(1)=6.83994507291
> celldm(3)=1.09801321247
> nat=5
> ntyp=3
> nbnd=26
> ecutwfc=60.0
> ecutrho = 600.0
> occupations = 'fixed'
> degauss=0.00
> /
> &electrons
> conv_thr = 1e-10,
> mixing_beta=0.3,
> /
> &IONS
> ion_dynamics='damp'
> bfgs_ndim=3
> pot_extrapolation = "second_order"
> wfc_extrapolation = "second_order"
> /
> &CELL
> cell_dynamics = 'damp-w',
> press = 0.0
> wmass = 0.02
> /
>
>
> But the calculation is not conversed and oscillate. The system has only five atoms
> and simple P4mm perovskite structure.
> I had change wmass as default value, but the convergence is not achieved.
> Is it too hard to converse to set forc_conv_thr = 1.0D-4 in VC-relax calculation ?
> ( I want to get severe internal atomic coordinate, and forc_conv_thr=1.0D-3 is not
> sufficient.) Simple atomic internal relaxation, I can get converged result.
>
>
> The stress and total force of output file is as follow.
>
> stress values ,,
>
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= -0.13
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= -2.09
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= -1.17
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= -0.60
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= 0.07
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= 0.37
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= 0.84
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= 0.95
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= 1.07
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= 1.22
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= 1.36
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= 1.47
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= 1.55
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= 0.96
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= 0.65
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= 0.39
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= 0.20
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= 0.04
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= -0.08
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= -0.13
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= -0.13
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= -0.63
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= -0.89
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= -1.05
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= -1.04
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= -1.13
>
>
> and The total force,
>
> Total force = 0.000512 Total SCF correction = 0.000057
> Total force = 0.000499 Total SCF correction = 0.000063
> Total force = 0.000472 Total SCF correction = 0.000024
> Total force = 0.000411 Total SCF correction = 0.000022
> Total force = 0.000385 Total SCF correction = 0.000053
> Total force = 0.000527 Total SCF correction = 0.000012
> Total force = 0.000487 Total SCF correction = 0.000188
> Total force = 0.000572 Total SCF correction = 0.000010
> Total force = 0.000537 Total SCF correction = 0.000016
> Total force = 0.000484 Total SCF correction = 0.000016
> Total force = 0.000440 Total SCF correction = 0.000007
> Total force = 0.000407 Total SCF correction = 0.000017
> Total force = 0.000369 Total SCF correction = 0.000016
> Total force = 0.000391 Total SCF correction = 0.000045
> Total force = 0.000552 Total SCF correction = 0.000015
> Total force = 0.000569 Total SCF correction = 0.000130
> Total force = 0.000683 Total SCF correction = 0.000026
> Total force = 0.000623 Total SCF correction = 0.000025
> Total force = 0.000544 Total SCF correction = 0.000020
> Total force = 0.000404 Total SCF correction = 0.000015
> Total force = 0.000280 Total SCF correction = 0.000028
> Total force = 0.000219 Total SCF correction = 0.000011
> Total force = 0.000348 Total SCF correction = 0.000039
> Total force = 0.000552 Total SCF correction = 0.000015
> Total force = 0.000688 Total SCF correction = 0.000019
> Total force = 0.000741 Total SCF correction = 0.000013
> Total force = 0.000723 Total SCF correction = 0.000013
> Total force = 0.000638 Total SCF correction = 0.000018
> Total force = 0.000504 Total SCF correction = 0.000017
> Total force = 0.000368 Total SCF correction = 0.000029
> Total force = 0.000256 Total SCF correction = 0.000020
> Total force = 0.001173 Total SCF correction = 0.000016
> Total force = 0.001841 Total SCF correction = 0.000271
> Total force = 0.001924 Total SCF correction = 0.000220
> Total force = 0.002328 Total SCF correction = 0.000057
> Total force = 0.002448 Total SCF correction = 0.000019
> Total force = 0.002318 Total SCF correction = 0.000016
> Total force = 0.002004 Total SCF correction = 0.000018
> Total force = 0.001547 Total SCF correction = 0.000022
> Total force = 0.001029 Total SCF correction = 0.000026
> Total force = 0.000669 Total SCF correction = 0.000015
> Total force = 0.002834 Total SCF correction = 0.000206
> Total force = 0.003057 Total SCF correction = 0.000170
> Total force = 0.001864 Total SCF correction = 0.000273
> Total force = 0.001107 Total SCF correction = 0.000101
> Total force = 0.000870 Total SCF correction = 0.000021
> Total force = 0.000355 Total SCF correction = 0.000068
> Total force = 0.000613 Total SCF correction = 0.000114
> Total force = 0.000484 Total SCF correction = 0.000038
> Total force = 0.000338 Total SCF correction = 0.000180
> Total force = 0.000372 Total SCF correction = 0.000125
> Total force = 0.000460 Total SCF correction = 0.000028
> Total force = 0.000482 Total SCF correction = 0.000014
> Total force = 0.000528 Total SCF correction = 0.000018
> Total force = 0.000652 Total SCF correction = 0.000008
> Total force = 0.000729 Total SCF correction = 0.000017
> Total force = 0.000740 Total SCF correction = 0.000013
> Total force = 0.000684 Total SCF correction = 0.000005
> Total force = 0.000573 Total SCF correction = 0.000005
> Total force = 0.000446 Total SCF correction = 0.000012
> Total force = 0.000369 Total SCF correction = 0.000010
> Total force = 0.000408 Total SCF correction = 0.000005
> Total force = 0.000602 Total SCF correction = 0.000044
> Total force = 0.000897 Total SCF correction = 0.000015
> Total force = 0.001145 Total SCF correction = 0.000020
> Total force = 0.001247 Total SCF correction = 0.000004
> Total force = 0.001348 Total SCF correction = 0.000050
>
> Sincerely.
>
>
> ----
> Yukihiro Okuno okunoyukihiro2000 at yahoo.co.jp
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