[Pw_forum] optimize monoclinic cell
Axel Kohlmeyer
akohlmey at cmm.chem.upenn.edu
Wed Apr 8 17:31:51 CEST 2009
On Wed, 2009-04-08 at 22:58 +0800, 程迎春 wrote:
> Thank you for your reply.
> Do you mean that I can neglect this numerical error?
i would not say "neglect". you have to be aware of it,
but you also have to consider that for as long as it is
within the error limits of your method, it would be
without negative consequences.
like for any numerical calculation there are no absolute
truths and the GIGO (=garbage-in, garbage-out) principle holds.
cheers,
axel.
>
>
> 2009/4/8 Axel Kohlmeyer <akohlmey at cmm.chem.upenn.edu>
> On Wed, 2009-04-08 at 19:01 +0800, 程迎春 wrote:
> > Dear Pwscf users,
> > I did a variable cell calculations for a base
> centered
> > monoclinic crystal. The cell displayed in xcrysden is
> correct, and
> > PWscf can find the symmetry. However, in the optimizing
> process, the
> > cell parameter changed unexpectedly, which may be wrong. In
> the
>
>
> no. it is most likely not wrong, but rather an indication of
> the
> level of numerical accuracy with which you computed your
> forces
> and stress tensor.
>
> cheers,
> axel
>
>
> > user's guide of PWscf, the base centered monoclinic cell is
> defined
> > as follows:
> > base centered monoclinic
> > =============================
> > v1 = ( a/2, 0, -c/2),
> > v2 = (b*cos(gamma), b*sin(gamma), 0),
> > v3 = ( a/2, 0, c/2),
> > where gamma is the angle between axis a and b
> > =============================
> > In the first step of optimize process, the cell is changed
> as
> > following:
> > CELL_PARAMETERS (alat)
> > 0.483414893 0.003687739 -0.271981740
> > -1.013180906 0.556415406 0.000000000
> > 0.483414893 0.003687739 0.271981740
> > My question is : why the quantities of second row of v1, v3
> vector do
> > not retain zero!
> >
> > Any suggestion and comment is appriciated. Thank you in
> advance!
> >
> > The input file is attached!
> > &CONTROL
> > title = 'c2',
> > prefix = 'li',
> > calculation = 'vc-relax' ,
> > restart_mode = 'from_scratch' ,
> > outdir = './' ,
> > wfcdir = './' ,
> > pseudo_dir = './' ,
> > tstress = .true. ,
> > tprnfor = .true. ,
> > etot_conv_thr = 1.0D-5,
> > forc_conv_thr = 1.0D-4,
> > /
> > &SYSTEM
> > ibrav = 13,
> > celldm(1) = 14.7756,
> > celldm(2) = 1.20528,
> > celldm(3) = 0.56348,
> > celldm(4) = -0.873177,
> > nat = 12,
> > ntyp = 1,
> > ecutwfc = 200,
> > nosym = .false. ,
> > /
> > &ELECTRONS
> > electron_maxstep = 100,
> > conv_thr = 1.D-10,
> > /
> > &IONS
> > ion_dynamics='bfgs',
> > /
> > &CELL
> > cell_dynamics='bfgs',
> > press=900,
> > /
> > ATOMIC_SPECIES
> > Li 6.914 Li.pz-s-mt.UPF
> > ATOMIC_POSITIONS (crystal)
> > Li -0.46080 0.21740 1.49640
> > Li -0.02770 0.02590 1.28350
> > Li -0.80760 0.63690 0.91840
> > Li 0.23010 0.43900 0.29270
> > Li 0.06870 0.87600 0.40410
> > Li -0.04760 0.70260 1.56000
> > Li -1.49640 -0.21740 0.46080
> > Li -1.28350 -0.02590 0.02770
> > Li -0.91840 -0.63690 0.80760
> > Li -0.29270 -0.43900 -0.23010
> > Li -0.40410 -0.87600 -0.06870
> > Li -1.56000 -0.70260 0.04760
> > K_POINTS automatic
> > 8 8 8 1 1 1
> >
> > --
> > Y. C. Cheng
> > Department of Phyics
> > Nanjing University
> > Nanjing 210093
> > P. R. China
> > Tel: 86-25-83592907
> > Email: yccheng.nju at gmail.com
> >
>
> > _______________________________________________
> > Pw_forum mailing list
> > Pw_forum at pwscf.org
> > http://www.democritos.it/mailman/listinfo/pw_forum
>
> --
> =======================================================================
> Axel Kohlmeyer akohlmey at cmm.chem.upenn.edu
> http://www.cmm.upenn.edu
> Center for Molecular Modeling -- University of
> Pennsylvania
> Department of Chemistry, 231 S.34th Street, Philadelphia, PA
> 19104-6323
> tel: 1-215-898-1582, fax: 1-215-573-6233, office-tel:
> 1-215-898-5425
> =======================================================================
> If you make something idiot-proof, the universe creates a
> better idiot.
>
> _______________________________________________
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>
>
>
> --
> Y. C. Cheng
> Department of Phyics
> Nanjing University
> Nanjing 210093
> P. R. China
> Tel: 86-25-83592907
> Email: yccheng.nju at gmail.com
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
--
=======================================================================
Axel Kohlmeyer akohlmey at cmm.chem.upenn.edu http://www.cmm.upenn.edu
Center for Molecular Modeling -- University of Pennsylvania
Department of Chemistry, 231 S.34th Street, Philadelphia, PA 19104-6323
tel: 1-215-898-1582, fax: 1-215-573-6233, office-tel: 1-215-898-5425
=======================================================================
If you make something idiot-proof, the universe creates a better idiot.
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