A modified X - Y method

The X - Y method seeks to solve the unknown phases of the X-ray reflections by minimizing a function (the X - Y function) of the phases. This cost function has been supplemented with a residual term. The total cost function is minimized by varying the positions of atoms. Simulated annealing is used to implement the minimization. Trial calculations for structures containing up to 176 non-H equal atoms have been carried out successfully.