Crystal structure determination by neutron powder diffraction using structural and packing constraints

Abstract

In the past, crystal structure determination of solids consisting of molecules (or atom groups) whose geometry and size are known approximately has often been attempted using neutron powder diffraction profile refinement techniques, but without inclusion of this information. A method of structure solution has therefore been developed to include it. The proposed method does not require a set of structure factors and thus avoids the problems encountered in separating peaks in a powder diffraction scan. A successful test was conducted with a previously determined (yet treated as unknown) crystal structure, where direct methods had failed to solve the structure due to incorrect peak separation.Two computer programs, MODEL and PARAM, that implement the method are described.

Pressure Dependence Investigation of the Low-Temperature Structure of TlAu(CN)2 by High-Resolution Neutron Powder Diffraction and Optical Studies

“…For such a large pseudosymmetric structure, it was decided to analyze the powder diffraction patterns with chemical structural constraints using the MORGUE program. , Nuclear neutron scattering amplitudes were taken from Sears . To limit the number of structural parameters, isotropic temperature factors were used, as this was considered a reasonable approximation at the sample temperature of approximately 62 K.…”

“…On the other hand, the longer neutron wavelength leads to a reduced number of contributing Bragg reflections (481 nonequivalent { hkl } reflections in the scattering angle range up to 140° used in the profile refinements). To limit the number of parameters we therefore used chemical constraints in the refinements, , similar to those in ref .…”

P-RISCON: a real-space scavenger for crystal structure determination from powder diffraction data

“…Some of the basic ideas underlying our project have already appeared in the recent literature, scattered, however, in different papers (see, for example, Reck, Kretschmer, Kutschabsky & Pritzkow, 1988;Rius & Miravitlles, 1988;Byrom & Lucas, 1991). Briefly, a three-dimensional translational search is performed and, if required, rotations of each model about three orthogonal axes are applied.…”