I've been struggling a bit to understand the definition of B-factors, particularly anisotropic Bs, and I think I've finally more-or-less got my head around the various definitions of B, U, beta etc, but one thing puzzles me.
It seems to me that the natural measure of length in reciprocal space is d* = 1/d = 2 sin theta/lambda but the "conventional" term for B-factor in the structure factor expression is exp(-B s^2) where s = sin theta/lambda = d*/2 ie exp(-B (d*/2)^2) Why not exp (-B' d*^2) which would seem more sensible? (B' = B/4) Why the factor of 4? Or should we just get used to U instead? My guess is that it is a historical accident (or relic), ie that is the definition because that's the way it is Does anyone understand where this comes from? Phil
