Using the t-distribution to improve the absolute structure assignment with likelihood calculations

The previously described method for absolute structure determination [Hooft, Straver & Spek (2008). J. Appl. Cryst. 41, 96-103] assumes a Gaussian error distribution. The method is now extended to make it robust against poor data with large systematic errors with the introduction of the Student t-distribution. It is shown that this modification makes very little difference for good data but dramatically improves results for data with a non-Gaussian error distribution.