It is well known that the isotropic x-ray scattering can be simulated from radial distribution functions (RDFs) which describe the ratio of local probability density to the bulk density, g(r) = ρ(r)/ρ . We define an 'atom type' as an element belonging to a certain region w of the system. Thus, e.g. an Oxygen belonging to the solute can be a different atom type than an Oxygen belonging to the solvent. For a pair of atom types l, m the pairwise RDF, g lm (r) can be sampled from molecular dynamics (MD) trajectories of i ∈ l and j ∈ m atom positions, sampled in spherical shells along r from the i'th particle to every j'th particle, δ(|r i -r j | -r):