Integrated intensities - missing the big picture ?

Kenneth Shankland ( (no email) )
Thu, 29 Jan 1998 12:11:28 +0000

In amongst discussions of the finer details of integrated
intensity vs. Rietveld, don't forget that we have used
integrated intensities as a means to an end in a
*structure solution* methodology. We don't see the need to fit
the entire profile for every trial structure, when we get the
same answer much faster using extracted intensities along with
the covariance matrix. When we are doing refinements of high
Tc's, GMR materials etc., we, like everyone else, do a Rietveld
refinement - one stage is easier than two in such situations.

We've put forward an approach that for the first time shows
how to solve structures with a high degree of internal
flexibility by global optimisation, on a time scale
that could be considered useful for routine applicability.
It therefore becomes a *viable* alternative to direct methods.

With a recent structure solution on a molecular structure,
we peaked at > 1000 structure refinements per second on
a lowly SGI O2. Maybe it'll go faster if I can figure out
the optimiser flags on the compiler. Anyone able to top that
using a full profile ?

Kenneth Shankland + Bill David

-- Dr. Kenneth Shankland,Building R3,ISIS Facility,Rutherford Appleton LaboratoryChilton,Didcot,Oxon OX11 0QX,United KingdomTel   : +44 1235 44 6381 Fax   : +44 1235 44 5720Email : k.shankland@rl.ac.uk