Depends on in what units you want to get your electron density in, or what scattering objects (electrons) you integrate over for the SF formula. Since the exponent is dimensionless in the SF formula, and the FT commonly is electron density,
electrons (not negative charge) has to be somewhere in the SF formula. If fo is in electrons, then f' and f" have to be units of electrons as well. The f' component reduces the real part scattering, it is negative (in electron units, again not in charge). BR -----Original Message----- From: CCP4 bulletin board [mailto:ccp...@jiscmail.ac.uk] On Behalf Of Tim Gruene Sent: Thursday, February 25, 2010 11:25 PM To: CCP4BB@JISCMAIL.AC.UK Subject: [ccp4bb] units of f0, f', f'' Dear all, I just stumbled across the question about what is the unit of f' and f''. The first couple of hits from ixquick.com claim it was e^-. Since e^- is not a unit but symbolises an elemtary particle (of which fractions are considered non-existent), I was wondering whether the unit of f, f', and f'' is actually e (a positive charge!) and the value of f^0 of Fe at its K-edge was actually 26e or -26e - see e.g. Table 1 in http://www.ccp4.ac.uk/courses/proceedings/1997/j_smith/main.html Cheers, Tim -- Tim Gruene Institut fuer anorganische Chemie Tammannstr. 4 D-37077 Goettingen GPG Key ID = A46BEE1A
