<DIV>Thank you, Stefaan<BR><BR><B><I>Stefaan Cottenier <Stefaan.Cottenier@fys.kuleuven.ac.be></I></B> wrote:
<BLOCKQUOTE class=replbq style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #1010ff 2px solid"><BR>> For the calculation of impurity doped 2*2*2 Ni3Al (L12 structure)<BR>supercell, which optimization is more important, E vs volume or E vs c/a?<BR><BR>Hard to say, it depends on the property. If the total energy is involved<BR>(for cohesive energy calculations, for instance), I expect E vs volume to be<BR>more important. For an EFG, c/a matter more. But experience shows that often<BR>you are very close to the global minimum if you optimize first the volume,<BR>and then c/a at your minimal volume.<BR><BR>In your case with an impurity, I would follow the following strategy:<BR><BR>1) optimize the volume of pure Ni3Al (not of the supercell).<BR>2) fix the minimal volume, and optimize c/a<BR>3) (if you have time, repeat 1) and 2) starting from the new c/a, until you<BR>find you are in the global minimum)<BR>4) make the supercell, insert the impurity<BR>5) relax the atoms !
that feel
forces due to the impurity (often very<BR>important! -- you didn't mention it in your question)<BR><BR>That is the fastest and quite safe procedure. If you would relax volume and<BR>c/a of the supercell containing the impurity already, it would in principle<BR>be a little bit more accurate: the a=b,c lattice constants that you find in<BR>this way will be somewhat different from the ones of pure Ni3Al, but they<BR>will mimic to some extent the displacements of the atoms that are far away<BR>from the impurity, outside your unit cell. (and here, in principle you have<BR>to relax neighbours at any volume or c/a ratio, very time consuming).<BR><BR>Stefaan<BR><BR>_______________________________________________<BR>Wien mailing list<BR>Wien@zeus.theochem.tuwien.ac.at<BR>http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien</BLOCKQUOTE></DIV><p><br><hr size=1><b>Do You Yahoo!?</b><br>
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