Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)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. (c) 2008 Elsevier B.V. All rights reserved.166SI2127Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Bundesministerium fur Forschung und Technologie (BMBF) [05 KS4KTC/1]HGF virtuelle Institut VH-VI 103 (Germany)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Bundesministerium fur Forschung und Technologie (BMBF) [05 KS4KTC/1]