Divide by 11 if you count all atoms, including H-atoms; divide by 20-22 if you only count non-H-atoms, to get the approximately number of atoms in the unit cell.
On Mon, May 5, 2014 6:07 am, Natalie Tatum wrote: > Hi all, > > I've had an interesting question from an undergradute student, asking if > there's any specific reference for the "18Ã rule of thumb" in small > molecule crystallography for dividing the volume of a unit cell by 18 for > the approximate number of non-hydrogen atoms. > > I'm afraid my google-fu has failed me, but I was curious as to whether > there is a reference associated with the practice of if it's just one of > those handy little pieces of advice for crystal screening. > > Thanks, > > Natalie
