Agradecimentos: ARBC is grateful to Prof I. Torriani (UNICAMP) for patient assistance regarding X-ray diffraction theory and SAXS, and for directing his attention to the publications of the Hamburg outstation of EMBL. Financial support by FAPESP (Fundacao de Amparo a Pesquisa do Estado de Sao Paulo, SP, Brazil), the Bundesministerium fur Forschung und Technologie (BMBF) under grant 05 KS4KTC/1 and from the HGF virtuelle Institut VH-VI 103 (Germany) are kindly acknowledged Ver menos

Abstract: In the context of direct imaging of single nanoparticles, we discuss strategies for simulation of the small angle X-ray scattering (SAXS) of nanoparticles, propose a new scalar numerical approach applicable to arbitrary collections of atoms and compare it to the existing alternatives, both scalar and vector. The simulations are also compared with SAXS experimental data obtained recently at the FLASH FEL in Hamburg (lambda(FEL) 32 nm), demonstrating the direct evaluation of size for very large Argon clusters with a single FEL pulse Ver menos