To people doing virtual crystal approximation
These last weeks, I tried to figure out whether the modified version of virtual.x was leading to reasonable pseudopotentials for VCA. Modified means simply that I removed the error message I have build 2 mixable pseudopotentials; same functional, same rinners, same number nature of wavefunctions and projectors. Then I mixed it uo using Virtual.x Apparently it works. You get an output pseudopotential with reasonable shape but there are many things wrong. - I compared the results of calculation with that potential with super-cell calculation with the same original potentials and the result if not completely different reveals a huge overestimate of the exchange splitting (I am calculating magnetic structures.) in the case of VCA. - More worrying, I mixed Co and Mn pseudopotentials in a 50/50 ratio and the results (again mainly the magnetisation) is completely different (40%) between 0.5xCo+0.5xMn and 0.5xMn+0.5xCo - Another trouble when I mixed Co and Mn with 100% of one of the two compounds. Then a mix of 100% Of Co (or Mn) is not equivalent to pure Co (or Mn) pseudo. I would say with my small experience that virtual.x is on the way to work but if you use it, do some simple tests before even if you thing that the resulting potential looks correct. Surprisingly, I got reasonable results mixing Fe and Co pseudo from pwscf library. As a conclusion and I am now trying to compare the two ways, for people doing VCA, I suggest building a new pseudopotential directly from Vanderbild code. Then, even if you get weird results, you have an access to all parameter of the pseudo generation If people have another experience on VCA with pwscf, please contact me. J?r?mie Jeremie Teyssier DPMC 24 quai Ernest Ensermet CH-1211 Geneve 4 SUISSE tel: (41) 22 379 35 68 fax: (41) 22 379 68 69 web: <http://optics.unige.ch/jeremie/home_jeremie.html> http://optics.unige.ch/jeremie/home_jeremie.html -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20071211/f6578d1b/attachment.htm
