LLM: a convolution-based algorithm to simulate the thermal diffuse X-ray scattering from protein crystals using the liquid-like-motion model

The still images of many protein crystals exposed to monochromatic X-rays show strong anisotropic diffuse scattering. The diffuse scattering is induced by correlated atomic disorder in the crystal and is called thermal diffuse scattering (TDS). The TDS has been successfully interpreted in several cases using the liquid-like-motion model. The model assumes that the degree of correlation of the mean atomic displacement decreases exponentially with the atomic pair separation, having a characteristic correlation length. The Fortran77 program LLM has been created to simulate the TDS on still images using this model and starting from a set of calculated crystallographic structure factors. It applies a convolution-based algorithm that mimics the mathematical description of the model.