Buy article online - an online subscription or single-article purchase is required to access this article.
computer programs
A quadratic approximation of the maximum-likelihood criterion is defined by a target value for every calculated structure-factor magnitude and the corresponding weight. These values can be estimated using the experimental structure-factor magnitudes and general information about the model imperfection. The program MLMF provides a user with these weights and target values. The obtained quadratic approximation allows one to carry out a kind of maximum-likelihood refinement by means of any least-squares refinement suite.