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On Wed, 2009-04-22 at 07:21 -0700, Álvaro Alves wrote:<BR>
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Hi all. I build a fully relativistic pseudopotencial for cobalt. When testing it I found the following results for lattice parameters: a = 2.44 A, c = 4.03 A and c / a = 1.65. The experimental values are 2.51 A, 4.07 A and 1.62. I want to improve these results. Do you have any suggestions? My input is below.<BR>
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alvaro,<BR>
<BR>
you can try sacrificing five chickens or a goat, bow five times to mecca or pray 5 ave marias.<BR>
<BR>
other than that, i'd say that you have a less than 3% overbinding for the lattice parameter<BR>
and 1% deviation in c and and since both errors are towards the same direction you have<BR>
an error of 2% in c/a. to the best of my knowledge, this is pretty much of what people report <BR>
as typical error margins for a gradient corrected functional, only that i remember seeing<BR>
underbinding more commonly than overbinding (the latter would be more common in LDA).<BR>
<BR>
at this point, the black magic of pseudopotential generation begins. you can twiddle with<BR>
cutoffs and electron configuration and see if this shifts the results closer to what you want,<BR>
while not harming transferability (how transferable is this potential anyways? did you test it?).<BR>
<BR>
cheers,<BR>
axel.<BR>
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--
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Axel Kohlmeyer <A HREF="mailto:akohlmey@cmm.chem.upenn.edu">akohlmey@cmm.chem.upenn.edu</A> <A HREF="http://www.cmm.upenn.edu">http://www.cmm.upenn.edu</A>
Center for Molecular Modeling -- University of Pennsylvania
Department of Chemistry, 231 S.34th Street, Philadelphia, PA 19104-6323
tel: 1-215-898-1582, fax: 1-215-573-6233, office-tel: 1-215-898-5425
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If you make something idiot-proof, the universe creates a better idiot.
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