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<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>To people doing virtual crystal approximation<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>These last weeks, I tried to figure out whether the modified
version of virtual.x was leading to reasonable pseudopotentials for VCA.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>Modified means simply that I removed the error
message…<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>I have build 2 mixable pseudopotentials; same
functional, same rinners, same number nature of wavefunctions and projectors.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>Then I mixed it uo using Virtual.x<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>Apparently it works. You get an output
pseudopotential with reasonable shape but there are many things wrong.<o:p></o:p></span></font></p>
<p class=MsoNormal style='margin-left:36.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo1'><![if !supportLists]><font
size=2 face=Arial><span lang=EN-GB style='font-size:10.0pt;font-family:Arial'><span
style='mso-list:Ignore'>-<font size=1 face="Times New Roman"><span
style='font:7.0pt "Times New Roman"'>
</span></font></span></span></font><![endif]><font size=2 face=Arial><span
lang=EN-GB style='font-size:10.0pt;font-family:Arial'>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.<o:p></o:p></span></font></p>
<p class=MsoNormal style='margin-left:36.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo1'><![if !supportLists]><font
size=2 face=Arial><span lang=EN-GB style='font-size:10.0pt;font-family:Arial'><span
style='mso-list:Ignore'>-<font size=1 face="Times New Roman"><span
style='font:7.0pt "Times New Roman"'>
</span></font></span></span></font><![endif]><font size=2 face=Arial><span
lang=EN-GB style='font-size:10.0pt;font-family:Arial'>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…<o:p></o:p></span></font></p>
<p class=MsoNormal style='margin-left:36.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo1'><![if !supportLists]><font
size=2 face=Arial><span lang=EN-GB style='font-size:10.0pt;font-family:Arial'><span
style='mso-list:Ignore'>-<font size=1 face="Times New Roman"><span
style='font:7.0pt "Times New Roman"'>
</span></font></span></span></font><![endif]><font size=2 face=Arial><span
lang=EN-GB style='font-size:10.0pt;font-family:Arial'>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.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>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.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>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…<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>If people have another experience on VCA with pwscf,
please contact me.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>Jérémie<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><st1:PersonName ProductID="Jeremie Teyssier" w:st="on"><strong><b><font
size=3 color=maroon face=Arial><span lang=EN-GB style='font-size:12.0pt;
font-family:Arial;color:maroon'>Jeremie Teyssier</span></font></b></strong></st1:PersonName><span
lang=EN-GB><o:p></o:p></span></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>DPMC</span></font><span lang=EN-GB><o:p></o:p></span></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>24 quai Ernest Ensermet</span></font><span
lang=EN-GB><o:p></o:p></span></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>CH-1211 Geneve 4</span></font><span lang=EN-GB><o:p></o:p></span></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>SUISSE</span></font><span lang=EN-GB><o:p></o:p></span></p>
<p class=MsoNormal><strong><b><font size=2 face=Arial><span lang=EN-GB
style='font-size:10.0pt;font-family:Arial'>tel: (41) 22 379 35 68</span></font></b></strong><span
lang=EN-GB><o:p></o:p></span></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>fax: (41) 22 379 68 69</span></font><span lang=EN-GB><o:p></o:p></span></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>web: </span></font><a
href="http://optics.unige.ch/jeremie/home_jeremie.html"><font size=2
color=maroon face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:maroon'>http://optics.unige.ch/jeremie/home_jeremie.html</span></font></a><o:p></o:p></p>
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