## Neutron Scattering Data Analysis 1990: Invited and Contributed Papers from the Conference on Neutron Scattering Data Analysis Held at The Rutherford Appleton Laboratory, Chilton, 14-16 March 1990 |

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Page 127

INTRODUCTION The use of neutron diffraction to study the magnetic properties

of 3d metal compounds leads to the determination of complex magnetic

structures. Several studies [1-6] have shown that it is necessary to have a

generalised refinement program to obtain the necessary fit to the resultant

magnetic structure. With powder data, since the list of measured reflections may

be short, it is especially important that all possible

order to reduce the number ...

INTRODUCTION The use of neutron diffraction to study the magnetic properties

of 3d metal compounds leads to the determination of complex magnetic

structures. Several studies [1-6] have shown that it is necessary to have a

generalised refinement program to obtain the necessary fit to the resultant

magnetic structure. With powder data, since the list of measured reflections may

be short, it is especially important that all possible

**constraints**be introduced inorder to reduce the number ...

Page 173

This

matrix is poorly conditioned. 4. Different types of data, e.g. neutron and X-ray

diffraction, can be modelled. The different data sets can have different Q ranges,

spacings, resolutions etc. It is also easy to include additional

structure; these could be from other experimental information (e.g. NMR) or could

be some other ,knowledge, of the system (e.g. chemical bonding ideas). 5. RMC

is ...

This

**constraint**,improves' the separation of partials in cases where the separationmatrix is poorly conditioned. 4. Different types of data, e.g. neutron and X-ray

diffraction, can be modelled. The different data sets can have different Q ranges,

spacings, resolutions etc. It is also easy to include additional

**constraints**on thestructure; these could be from other experimental information (e.g. NMR) or could

be some other ,knowledge, of the system (e.g. chemical bonding ideas). 5. RMC

is ...

Page 219

CONSTRAINED MODEL FITTING In the examples presented so far we have

used model fitting with no

surface chemistry it is possible to impose

first of these results forms the large difference in scattering powers for neutrons

between protons and deuterons. Hydrogen-deuterium isotopic substitution can

therefore be used in chemical systems to manipulate the refractive index profile.

CONSTRAINED MODEL FITTING In the examples presented so far we have

used model fitting with no

**constraints**imposed. In the investigation of problems insurface chemistry it is possible to impose

**constraints**upon the model fitting. Thefirst of these results forms the large difference in scattering powers for neutrons

between protons and deuterons. Hydrogen-deuterium isotopic substitution can

therefore be used in chemical systems to manipulate the refractive index profile.

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algorithm applications approach atoms Bayesian beam Bragg peaks calculated configuration constraints coordinates corresponding cost function cross-section crystallographic Data Anal data analysis data set defined detector bank determined diffraction data diffractometer distribution function elastic scattering energy error bars example experiment experimental Figure Fourier transform Gaussian GENIE GENIE-V3 histogram inelastic instrument intensity inverse ISIS least squares likelihood function magnetic structure magnetisation density matrix MaxEnt reconstruction Maximum Entropy McGreevy measured method molecular Monte Carlo neutron diffraction neutron scattering normalisation normalization obtained optimisation optimization problems parameters Patterson map performed Phys plot positive powder diffraction presented at Neutron prior procedure quasielastic radial distribution functions refinement reflectivity data resolution function ROTAX Rutherford Appleton Laboratory sample scan scattering law shown simulated annealing single crystal solution spectra spectrometer spectrum statistical structure factor symmetry technique temperature time-of-flight truncation UNIRAS unit cell vanadium vector wavelength workspace