<div>Thank you for your reply.</div>
<div>Do you mean that I can neglect this numerical error?<br><br></div>
<div class="gmail_quote">2009/4/8 Axel Kohlmeyer <span dir="ltr"><<a href="mailto:akohlmey@cmm.chem.upenn.edu">akohlmey@cmm.chem.upenn.edu</a>></span><br>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">
<div class="im">On Wed, 2009-04-08 at 19:01 +0800, 程迎春 wrote:<br>> Dear Pwscf users,<br>> I did a variable cell calculations for a base centered<br>> monoclinic crystal. The cell displayed in xcrysden is correct, and<br>
> PWscf can find the symmetry. However, in the optimizing process, the<br>> cell parameter changed unexpectedly, which may be wrong. In the<br><br></div>no. it is most likely not wrong, but rather an indication of the<br>
level of numerical accuracy with which you computed your forces<br>and stress tensor.<br><br>cheers,<br> axel<br>
<div>
<div></div>
<div class="h5"><br>> user's guide of PWscf, the base centered monoclinic cell is defined<br>> as follows:<br>> base centered monoclinic<br>> =============================<br>> v1 = ( a/2, 0, -c/2),<br>
> v2 = (b*cos(gamma), b*sin(gamma), 0),<br>> v3 = ( a/2, 0, c/2),<br>> where gamma is the angle between axis a and b<br>> =============================<br>> In the first step of optimize process, the cell is changed as<br>
> following:<br>> CELL_PARAMETERS (alat)<br>> 0.483414893 0.003687739 -0.271981740<br>> -1.013180906 0.556415406 0.000000000<br>> 0.483414893 0.003687739 0.271981740<br>> My question is : why the quantities of second row of v1, v3 vector do<br>
> not retain zero!<br>><br>> Any suggestion and comment is appriciated. Thank you in advance!<br>><br>> The input file is attached!<br>> &CONTROL<br>> title = 'c2',<br>
> prefix = 'li',<br>> calculation = 'vc-relax' ,<br>> restart_mode = 'from_scratch' ,<br>> outdir = './' ,<br>
> wfcdir = './' ,<br>> pseudo_dir = './' ,<br>> tstress = .true. ,<br>> tprnfor = .true. ,<br>> etot_conv_thr = 1.0D-5,<br>
> forc_conv_thr = 1.0D-4,<br>> /<br>> &SYSTEM<br>> ibrav = 13,<br>> celldm(1) = 14.7756,<br>> celldm(2) = 1.20528,<br>> celldm(3) = 0.56348,<br>
> celldm(4) = -0.873177,<br>> nat = 12,<br>> ntyp = 1,<br>> ecutwfc = 200,<br>> nosym = .false. ,<br>
> /<br>> &ELECTRONS<br>> electron_maxstep = 100,<br>> conv_thr = 1.D-10,<br>> /<br>> &IONS<br>> ion_dynamics='bfgs',<br>> /<br>> &CELL<br>
> cell_dynamics='bfgs',<br>> press=900,<br>> /<br>> ATOMIC_SPECIES<br>> Li 6.914 Li.pz-s-mt.UPF<br>> ATOMIC_POSITIONS (crystal)<br>> Li -0.46080 0.21740 1.49640<br>> Li -0.02770 0.02590 1.28350<br>
> Li -0.80760 0.63690 0.91840<br>> Li 0.23010 0.43900 0.29270<br>> Li 0.06870 0.87600 0.40410<br>> Li -0.04760 0.70260 1.56000<br>> Li -1.49640 -0.21740 0.46080<br>> Li -1.28350 -0.02590 0.02770<br>
> Li -0.91840 -0.63690 0.80760<br>> Li -0.29270 -0.43900 -0.23010<br>> Li -0.40410 -0.87600 -0.06870<br>> Li -1.56000 -0.70260 0.04760<br>> K_POINTS automatic<br>> 8 8 8 1 1 1<br>><br>
> --<br>> Y. C. Cheng<br>> Department of Phyics<br>> Nanjing University<br>> Nanjing 210093<br>> P. R. China<br>> Tel: 86-25-83592907<br>> Email: <a href="mailto:yccheng.nju@gmail.com">yccheng.nju@gmail.com</a><br>
><br></div></div>> _______________________________________________<br>> Pw_forum mailing list<br>> <a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br>> <a href="http://www.democritos.it/mailman/listinfo/pw_forum" target="_blank">http://www.democritos.it/mailman/listinfo/pw_forum</a><br>
<br>--<br>=======================================================================<br>Axel Kohlmeyer <a href="mailto:akohlmey@cmm.chem.upenn.edu">akohlmey@cmm.chem.upenn.edu</a> <a href="http://www.cmm.upenn.edu/" target="_blank">http://www.cmm.upenn.edu</a><br>
Center for Molecular Modeling -- University of Pennsylvania<br>Department of Chemistry, 231 S.34th Street, Philadelphia, PA 19104-6323<br>tel: 1-215-898-1582, fax: 1-215-573-6233, office-tel: 1-215-898-5425<br>=======================================================================<br>
If you make something idiot-proof, the universe creates a better idiot.<br><br>_______________________________________________<br>Pw_forum mailing list<br><a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br><a href="http://www.democritos.it/mailman/listinfo/pw_forum" target="_blank">http://www.democritos.it/mailman/listinfo/pw_forum</a><br>
</blockquote></div><br><br clear="all"><br>-- <br>Y. C. Cheng<br>Department of Phyics<br>Nanjing University<br>Nanjing 210093<br>P. R. China<br>Tel: 86-25-83592907<br>Email: <a href="mailto:yccheng.nju@gmail.com">yccheng.nju@gmail.com</a><br>