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A Bernoullian powder sample is defined as an ensemble of parallelepiped crystals where the probability of any layer being on the surface is independent of its size as well as of the number of its predecessors, although being different for the three types of layers parallel to the crystal faces....
The newly developed fast Fourier least-squares algorithm Agarwal (1978). Acta Cryst. A34, 791-809 has been used to refine the structure of rhombohedral 2-Zn pig insulin at a resolution of 1.5 A. The CPU time required for each cycle of refinement was about 3 min on an IBM 370/168 computer. After...
The intensity of X- ray scattering from f.c.c. crystals containing extrinsic stacking faults with two fault parameters see Howard (1977). Acta Cryst. A33, 29-32 has been calculated.
Phase refinement based on minimization of C = h, k |EhEkE-h-k | 1 -- cos(h + k + -h-k)2 has been tested on several known structures (space group P21) containing elements of pseudo-centrosymmetry. C always has a maximum for a consistent centric phase set provided that some invariants have a phase...
Room temperature X - N difference electron density maps are calculated for the non-centrosymmetric lithium formate monohydrate, a potential ferroelectric, by taking the phases appropriate to Fo,x as those calculated from a multipole deformation density refinement Hirshfeld (1971). Acta Cryst....
The compound Bi2Fe4O9 belongs to the space group Pbam ( D92h), with two formula units per unit cell. Neutron diffraction measurements showed that it is paramagnetic at room temperature and undergoes a transition to an antiferromagnetic state at TN = (264 plus or minus 3) K in agreement with...
It is shown that correlation between the third-cumulant coefficients in noncentrosymmetric structures restricts the number of coefficients which can be refined. In the space group P1 all ten coefficients of one atom have to be kept fixed.
A simple test for the validity of the rigid-body model for molecular vibrations in crystals is proposed.
A fast-converging mathematical method for calculation of convolution square roots of one-dimensional functions has been developed. Application to one-dimensional periodic structure projections as well as to non-periodic structures is possible. Computer calculations of some examples are given.
A new two-wavelength Bijvoet-pair method is proposed, which allows unique experimental determination of anomalous phases without absorption correction and scaling of the Bragg intensities, if the resonant atom structure is known. The method consists of measuring Bijvoet ratios at two wavelengths...
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