[Pw_forum] optimize monoclinic cell

[程迎春]

Thank you for your reply.
Do you mean that I can neglect this numerical error?

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
> >
> > _______________________________________________
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> > 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
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