A small-angle scattering model for broad correlation peaks and small diffuse scattering.

Porous and/or bicontinuous structures often display a pronounced correlation peak in their small-angle scattering that indicates a preferred domain spacing d. A first attempt to describe the full q dependence of small-angle scattering profiles has been formulated in a previous publication [Frielinghaus (2026) J. Appl. Cryst. 59, 837-844]. However, the diffuse scattering, i.e. the forward scattering, is often found to be lower than in this simple framework, while the correlation peak is rather broad. By adding one more parameter σ that stretches the correlation peak with respect to the residual features of the theory, a more general heuristic theoretical framework for porous and/or bicontinuous structures is obtained. The predominant conditions and their physical meaning are discussed in context with practical examples.