th2_offset definition?

rowlesmr

How is th2_offset* defined?

2Th_actual = 2Th_measured + th2_offset
or
2Th_measured = 2Th_actual + th2_offset
or
something else?

Cheary & Coelho define
epsilon = 2Th_measured - 2Th_actual
Is epsilon == th2_offset?

*I know that it should really be x_offset, but most data is 2theta on the x-axis, so....

johnsoevans

Lazy answer: I never bother trying to remember this. Can't you just type in an offset value and see what happens to your calculated pattern? (I've a feeling I might have missed the point as that answer seems a bit easy for a rwolesmr question!)

rowlesmr

Lazy question, too 🙂

rowlesmr

Figured it out:

yobs_eqn row119.xy = Gauss(10.1, 1);   min -2 max 20 del 0.01
     
lam
  ymin_on_ymax 0.0001
  la 1 lo 1  lh 0.00001   

Zero_Error(@, 0.0999998495`)
     
xo_Is
	xo 10 I @  0.999983638`
	peak_type pv
		pv_lor 0
		pv_fwhm @  1`

If I draw a gaussian at 10.1, and fit it with a gaussian fixed at 10, the refined offset is 0.1.

2Th_obs = 2Th_calc + offset

2Th_calc = 2Th_obs - offset

This means that if you want to write out an XY file with corrected 2Th values, you need to subtract any offsets from the data values you've read in.

I'll have to write a macro for that. 🙂

rowlesmr

Here you go:

macro Out_X_Xcorr_Yobs_Ycalc(file, & ze, & sd)
{
	xdd_out file load out_record out_fmt out_eqn
	{
		" %11.6f  " = X;
		" %11.6f  " = X - (ze - 2 Rad sd Cos(X Deg_on_2) / Rs);
		" %11.6f  " = Yobs;
		" %11.6f\n" = Ycalc;
	}
}