Le lundi 30 juillet 2007 à 09:04 +0300, Jonas Frantz a écrit : > Hi, > > the problem here is that bodr is defining the vectors for each element, this > is > completely redundant as most of the crystal structures can be described as a > function of lattice structure (hcp, fcc, bcc and so on), the length of the > unit > cell vectors a,b,c and the angles of these alfa, beta, gamma. This would allow > full description of the more exotic crystal structures as well. Have a look at > for instance http://www.webelements.com/webelements/elements/text/Si/xtal.html > for a source of these parameters.
You might notice that they also give the space group, not the Bravais lattice. > The vectors for each crystalstructure can then be described as the vectors for > each atom within the unit cell and the unitvectors. > > What this is practice means: > - Reduce the crystalstructure.xml to only contain the separate > crystalstructures > with unitvectors in terms of the lattice constant. > - Introduce a couple of new fields per element in elements.xml. > > Regarding introducing the new fields to elements.xml, I guess you would want > to > do it in this fashion (note that for fcc all vectors are equal): > > <lattice abundance="1.0"> > <label name="structure" value="fcc" /> > <scalar name="lattice_a" value="3.564" unit="angstrom" /> > <scalar name="lattice_b" value="3.564" unit="angstrom" /> > <scalar name="lattice_c" value="3.564" unit="angstrom" /> > <scalar name="lattice_alfa" value="90" unit="degrees" /> > <scalar name="lattice_beta" value="90" unit="degrees" /> > <scalar name="lattice_gamma" value="90" unit="degrees" /> > </lattice> With those data, you need the position of the second Si atom. If you have the space group, you don't. Anyway, atomic position are needed at least for molecular crystals, as hydrogen, since the origin in that case is not at an atomic position and there is no translation (in the space group) from one atom to the other (in that case, probably one atom is enough, since they are related by a symmetry operation). Even some metals need atomic position, as Mn alpha. > By using this structure, you could describe all of the existing structures for > every element (the sum of the abundance parameters should of course be 1). ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Blueobelisk-discuss mailing list Blueobelisk-discuss@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/blueobelisk-discuss
