[Wien] a serious problem about optimization of hexagonal cell

Chandrika rcais at cal3.vsnl.net.in
Mon Aug 6 06:15:59 CEST 2007


Dear Mary,
If your structure has a lot of forces you will need to do  MINI first to optimize xyz positions.
Also you could check other ground state properties like cell parameters, c/a, DOS etc. This would give you a clue about any possible input errors.
Hope this helps,
Chandrika
  ----- Original Message ----- 
  From: Mary White 
  To: wien2k 
  Sent: Saturday, August 04, 2007 2:59 PM
  Subject: [Wien] a serious problem about optimization of hexagonal cell


  Dear all users,
       Nowadays,I'm focused on the optimization of hexagonal cell. I know using full-potential method to optimize the hexagonal or the orthogonal cell is a little trouble. But I really know how to do this. I have learned the optimization notes in the web of WIEN2K.I minimized atomic positions and lattice constants as the notes said. 
       First, I used the experimental structure on a high pressure phase to optimize the c/a,for example -4,-2,0,2,4 as the notes says. Then I plot the E vs c/a.The plot isn't a perfectly parabolic.But the minimum of energy is still canbe found. So I continue to start a loop over the five c/a ratios. Five c/a correspond to five different structures,as to every structure,I optimize the  volumes. So, as to every a c/a, I can plot E~V parabolic,that is,I can get five energy and correspond volumes,these are all the minimum energy on the parabolic lines.But when I use these datas to get the EOS,the value of B0 is not coincide with the value got from the pseudo-potential method.And the finally E~V is a similar line.The range of pressure got from EOS is very small,almost a same pressure.I am puzzled with that.
        I want to know whether the method and process I used is right.If something wrong,how I can do ?  I am sorry to waste you so much time. I think the optimization of hexagonal cell is a generalized problem,so if anyone knows,please give me some advise.Any comments will be appreciated.Thank you in advance.Thanks a lot.
                                                                                         Mary



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