From: Alan H. <he...@il...> - 2006-09-26 15:07:41
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<html> <body> Firstly, I was wrong :-) in thinking that Jmol does not have access to different ionic radii for different valence states (thanks Angel and Phillip). Bob's table radii.xls does indeed contain the various valence states. But does Jmol actually use the valence states specified in CIF files ? eg:<br> <pre>_atom_type_oxidation_number As3- -3. Na1+ 1. </pre>For example, as Angel's table shows:<a href="http://biomodel.uah.es/jmol/radii/jmol_radii.en.html" eudora="autourl"> http://biomodel.uah.es/jmol/radii/jmol_radii.en.html</a><br> there should be a big difference between As-3 <br> <a href="http://icsd.ill.fr/icsd/index.php?action=Search&elements=as-3" eudora="autourl"> http://icsd.ill.fr/icsd/index.php?action=Search&elements=as-3</a> <br> as in Na3As, and As+3 as in CsAs4F13<br> <a href="http://icsd.ill.fr/icsd/index.php?action=Search&elements=as%2B3" eudora="autourl"> http://icsd.ill.fr/icsd/index.php?action=Search&elements=as%2B3<br> </a>I have taken those examples because there can be no doubt about the valence state of As, it is clearly marked in the CIF files, and these files are freely available from the demo WWW version of ICSD.<br><br> For CIF files, Jmol draws As-3 with much the same radius as As+3. I suspect it is using the uncharged atom radius, so As-3 and As+3 are drawn the same size, intermediate between Na+1 and Cs+1<br><br> Alan.<br> BTW, David Brown tells me that the best values for ionic radii are still those of Shannon and Prewitt 1969, Acta Cryst. B25, 925-946 (for oxides) and Shannon 1976 Acta Cryst. A32, 751-767 (for halides), so I guess the values in Jmol are fine (I haven't checked).<br> </body> <br> <div>_____________________________________________________________</div> <div>Dr Alan Hewat, ILL Grenoble, FRANCE<he...@il...>fax+33.476.20.76.48</div> <div>+33.476.20.72.13 (.26 Mme Guillermet) <a href="http://www.ill.fr/dif/people/hewat/" EUDORA=AUTOURL> http://www.ill.fr/dif/people/hewat/</a></div> <div>_____________________________________________________________</div> </html> |