Pepsi-SAXS: an adaptive method for rapid and accurate computation of small-angle X-ray scattering profiles

Abstract

A new method calledPepsi-SAXSis presented that calculates small-angle X-ray scattering profiles from atomistic models. The method is based on the multipole expansion scheme and is significantly faster compared with other tested methods. In particular, using the Nyquist–Shannon–Kotelnikov sampling theorem, the multipole expansion order is adapted to the size of the model and the resolution of the experimental data. It is argued that by using the adaptive expansion order, this method has the same quadratic dependence on the number of atoms in the model as the Debye-based approach, but with a much smaller prefactor in the computational complexity. The method has been systematically validated on a large set of over 50 models collected from the BioIsis and SASBDB databases. Using a laptop, it was demonstrated thatPepsi-SAXSis about seven, 29 and 36 times faster compared withCRYSOL,FoXSand the three-dimensional Zernike method inSAStbx, respectively, when tested on data from the BioIsis database, and is about five, 21 and 25 times faster compared withCRYSOL,FoXSandSAStbx, respectively, when tested on data from SASBDB. On average,Pepsi-SAXSdemonstrates comparable accuracy in terms of χ2toCRYSOLandFoXSwhen tested on BioIsis and SASBDB profiles. Together with a small allowed variation of adjustable parameters, this demonstrates the effectiveness of the method.Pepsi-SAXSis available at http://team.inria.fr/nano-d/software/pepsi-saxs.