G(hkl) = (h^2*L11+k^2*L22+l^2*L33+2*h*k*L12+2*h*l*L13+2*k*l*L23)d^3
for neutron TOF data and gives the Lorentzian microstrain broadening in
musec for a given reflection according to its hkl. Getting the mustrain
itself involves computing this function for a variety of hkl's and dividing
each by DifC (d to TOF conversion constant) and plotting it - it's a 3-D
surface with frequently some kind of "dumbbell" appearance. Following the
discussion on p. 132-3 of the GSAS manual use
S(hkl) = G(hkl)/C
For CW data (x-ray or neutron) the function is similar
G(hkl) = (h^2*L11+k^2*L22+l^2*L33+2*h*k*L12+2*h*l*L13+2*k*l*L23)d^2*tan(th)
Getting the mustrain for a particular hkl then follows the discussion on
p.136-7 of the GSAS manual where
S(hkl) = G(hkl)*pi/18000
This can be plotted as above as a 3-D surface and will probabaly have a
dumbell like appearance.
There has been a new development in GSAS in this area with the help of
Peter Stephens (SUNY StonyBrook). At the last EPDIC meeting (Parma) he
described a more soundly based description of anisotropic strain
broadening. I have recently implemented his description in PC-GSAS and will
be releasing it soon. His description is better than the Lij one presently
in GSAS. More about this later.
Bob Von Dreele