Peak profiles¶

A profile turns an integrated reflection contribution into intensity over a powder-pattern axis. Its width and asymmetry are part of the experiment model.

• Constant wavelength: Gaussian, Lorentzian, direct pseudo-Voigt, TCH, Bérar–Baldinozzi and Finger–Cox–Jephcoat.
• Time of flight: symmetric pseudo-Voigt, Jorgensen and Jorgensen–Von Dreele.

The catalogue lists the exact supported type tokens. A similarly named type from another program is not sufficient to establish matching width, mixing or asymmetry conventions.

Width and normalisation¶

A unit-area profile integrates to one over its complete mathematical domain. Peak height therefore changes as width changes, even when integrated intensity remains fixed. FWHM \(H\) and Gaussian standard deviation \(\sigma\) satisfy \(H=\sqrt{8\ln2}\,\sigma\).

Finite peak windows¶

The evaluated pattern can use a finite window set by a cutoff in FWHM units. Tails outside that window are omitted; a finite window is a calculation choice rather than a new physical profile. The current window extent is cutoff_fwhm * H; a nonpositive cutoff selects the full-range path. Keep the cutoff when comparing calculations, particularly for Lorentzian tails.