[Wien] a serious problem about optimization of hexagonal cell

[Mary White]

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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