Hello, I am having difficulties in understanding the "sig" parameter in GSAS 2 under "Reflection List". I believe GSAS 2 is showing the square of the gaussian fwhm component of the pseudo Voigt function, sig = U*tan^2(theta) + V*tan(theta) + W, in centidegrees. In fact, when using U, V and W from "Instrument Parameters" I arrive at the value of sig in "Reflection List". . The problem is that the value of "sig" showed by GSAS is quite different from the value I get when using another program, for example the XPert HighScore. See example below. (Note that the "gam" values match) . sqrt(sig) gam fwhm GSAS 1.7219 6.7518 7.043 Xpert 3.584 6.777 8.37 . To calculate the last column, I used : fwhm = Sum(i=0 to 5) [Ki * G^[5-i] * L^i], in which G = sqrt(sig) and L = gam. This is the number 3 equation in Thompson, Cox and Hastings, J. Appl. Cryst. (1987) 20, 79-83. . Visually the fits from both GSAS and Xpert are pretty good, so I was wondering if GSAS is adding/subtracting something else in "sig". I appreciate your help.

Sincerely, Marcus A. R. Miranda Universidade Federal do CearĂ¡ - UFC

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