[Wien] a serious problem about optimization of hexagonal cell

[Mary White]

Dear Chandrika,
Thank you for your suggestion.I will examine the whole process as your suggestions.

Chandrika <rcais at cal3.vsnl.net.in> wrote:       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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