luciamaini
Dear all,
I'm refining a structure in the space group R3m described with an hexagonal cell.
Since TCHZ peak shape is not optimal ( some peaks are broad and some are narrow) I tried the Stephens anistropic strain
I adpated the macro for the Trigonal for hexagonal indeces following the article
P. W. Stephens, J. Appl. Crystallogr., 1999, 32, 281–289
the macro I wrote is this one:
macro Stephens_trigonal_R3 (s400,s202,s004,s301,eta)
{
prm mhkl = H^4 s400 + K^4 s400 + L^4 s004 +
3 ( H^2 K^2 3 s400 + H^2 L^2 s202 + K^2 L^2 3 s400) +
2 ( H K^3 2 s400 + H^3 L s301 + K L^3 2 s400)+
3 ( H^2 K L 3/2 s301 - H K^2 L 3/2 s301 + H K L^2 s202);
prm pp = D_spacing^2 * Sqrt(Max(mhkl,0)) / 1000;
gauss_fwhm = 1.8/3.1415927 pp (1-eta) Tan(Th) + 0.0001;
lor_fwhm = 1.8/3.1415927 pp eta Tan(Th) + 0.0001;
}
I hope it is correct ! it works ( no syntax errors)
But I have problem to define the parameter s400,s202,s004,s301
I started with an equal value for all parameters (prm=100) and let them refining or should I get the starting value from somewhere?
are negative parameters acceptables?
Thank you
Lucia
alancoelho
To define s400 for example the use:
prm s400 #start min #min max #max
where #start, #min, #max are numbers corresponding to the starting, minimum expected value and maximum expected value.
Also, eee the section in the Technical Reference how to define a parameter