Direct solutions of the Si(111) 7x7 structure

We show that it is possible to use direct methods to solve surface structures as complicated as that of the si(111) 7 x 7. The first of these methods is maximum entropy combined with likelihood estimation, the second a combination of symbolic phasing methods and weakly interpolating modifications of the Sayre equation. These techniques are applied to two different elements of the structure determination, namely ab initio structure determination solely from diffraction intensity data and phase extension from a set of known phases derived from high resolution images. (C) 1997 Elsevier Science B.V.