Approaches to modeling diffuse scattering from molecular crystals: para-terphenyl (C 18 H 14 )

Abstract

Diffuse scattering is a probe of the local correlations in a crystal, whereas Bragg peaks are descriptive of the average long-range ordering. The long-range average is the result of numerous local configurations the population of which cannot be determined from the Bragg peaks. Diffuse scattering can examine this population. This is particularly the case when making use of the three-dimensional distribution of diffuse scattering from single crystals. However, diffuse scattering is very weak and broad and is often of similar intensity to the experimental background, which makes data collection demanding. Disorder can also take many forms and local configurations are not constrained by the average crystallographic symmetry. Here, three approaches to the modeling of diffuse scattering from molecular crystals will be discussed. All three approaches are based on a Monte Carlo (MC) simulation. As an example, the modeling of neutron diffuse scattering from para-terphenyl (PTP, C 18H14) will be described.