Dear all I am a chemist that uses xrd-powder diffraction to follow the course of reactions. Therefore, mass-fractions or number of atoms per unit cell are not useful to me. I deal with mol fractions of formula units (FU). To convert from the unit cell related values to FU related values I need to know the number of FUs per unit cell (Z). How can I calculate this based solely on the information stored in a gsas-II project (I want to use scriptable to automate the task).
So far I seem to have a solution but I am not sure if it is really correct: For each phase, the greatest common divisor (GCD) of the site multiplicity of all atoms corresponds to Z. As example LaFeO3 (Pnma): La 4 Fe 4 O1 8 O2 4 Formula per unit cell: La4Fe4O12 GCD=4 -> FU=LaFeO3 This also gives the correct FU for solid solutions like Ce0.1Ce0.9O2. But there are cases where more than one atom form the basis as e.g. graphite(P63/mmc): C1 2 C2 2 Formulat per unit cell: C4 GCD=2 -> FU=C2 Here I miss the factor 2 due to the 2-atom basis. How do I identify a n-atom basis? I assume that in this case I would find for each atom n sets that have the identical multiplicity. In the case of the LaFeO3 example above a second set with La/4, Fe/4, O1/8, O2/4 would have to be present. So the question: Is my solution generic and correct? Thanks for any help / suggestions -- Dr. Ivo Alxneit Applied Catalysis and Spectroscopy Group Bioenergy and Catalysis Laboratory phone: +41 56 310 4092 Paul Scherrer Institute fax: +41 56 310 2688 CH-5232 Villigen gnupg key: 0x515E30C7 Switzerland https://www.psi.ch/acs/
signature.asc
Description: OpenPGP digital signature
_______________________________________________ GSAS-II mailing list [email protected] https://mailman.aps.anl.gov/mailman/listinfo/gsas-ii
