Temp

GSAS offers 5 different Constant Wavelength (CW) X-ray profile functions. They are described in detail within the GSAS technical manual (see page 156). 11-BM users are encouraged to use either profile type 3 or type 4.

A quick reference for the various profile type 3 and 4 terms is given below. Users are strongly encouraged to read this section of the GSAS manual at least once before (or after) blindly using this guide!

These peak profile functions are a pseudo-Voigt type, combining Gaussian (G) and Lorentzian (L) components.

The general Gaussian shape (as a function of angle θ) is described by the Cagliotti function

Gaussian Profile ≈ U*tan2θ + V*tanθ + W + P/cos2θ

These U, V, W, and P variables match the GU, GV, GW, and GP profile terms you see below.

11-BM users will not (usually) need to change or refine these values.

Constant Wavelength X-ray GSAS Profile Type 3

GU = Gaussian U term	GV = Gaussian V term	GW = Gaussian W term
GP = Gaussian crystallite size broadening	LX = Lorentzian crystallite size broadening	LY = Lorentzian strain broadening
S/L = Finger-Cox Axial Divergence S term	H/L = Finger-Cox Axial Divergence H term	trns = sample transparency
shft = sample displacement	stec = anisotropic strain	ptec = anisotropic crystallite size
sfec = sublattice anisotropic broadening (stacking faults)	LXX = Lorentzian microstrain anisotropy	LYY = Lorentzian microstrain anisotropy

Constant Wavelength X-ray GSAS Profile Type 4

GU = Gaussian U term	GV = Gaussian V term	GW = Gaussian W term
GP = Gaussian crystallite size broadening	LX = Lorentzian crystallite size broadening	ptec = anisotropic crystallite size
trns = sample transparency	shft = sample displacement	sfec = sublattice anisotropic broadening (stacking faults)
S/L = Finger-Cox Axial Divergence S term	H/L = Finger-Cox Axial Divergence H term	eta = mixing factor, from pure Gaussian (0) to pure Lorentzian (1)
SXXX = Stephens anisotropic microstrain broadening	SYYY = Stephens anisotropic microstrain broadening	SZZZ = Stephens anisotropic microstrain broadening