Abstract

The simple `weighted sum formula' has been studied as regards its applicability to phase refinements. These studies show that proper weighting of the phase relations significantly improves the phase estimates from phase-sum formulae. The evaluation of weights used in the `variance-weighted sum formula' is discussed, together with the problem of the 2 ambiguity. A simple procedure for selecting efficient basis sets is also given. The procedures described have been programmed and used to solve twelve unknown structures. Applications to somewhat complicated cases are described.