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The space-group distribution of molecular organic structures
Wilson, A. J. C., Karen, V. L. and Mighell, A.  International Tables for Crystallography (2006). Vol. C, ch. 9.7, pp. 897-906 [ doi:10.1107/97809553602060000623 ]
... distribution of molecular organic structures is reviewed. Topics discussed include: a priori classifications of space groups; special positions of given symmetry ... space-group frequencies; the use of molecular symmetry; structural classes; a statistical model for space-group frequency; molecular packing; and a priori predictions of molecular crystal structures. 9.7.1. A priori ...

Factors determining accuracy
Parrish, W., Wilson, A. J. C. and Langford, J. I.  International Tables for Crystallography (2006). Vol. C, Section 5.2.13, pp. 501-504 [ doi:10.1107/97809553602060000596 ]
... to 0.0001% is rarely reached and each determination is virtually a research project. The more important factors are: (1) Differentiation of ... the term, the error in [Delta]d is smaller for a given angular accuracy . The gain is not as great ... and (iv) fewer problems of overlapping. In any particular case, a balance of advantage must be sought. The forward reflections ...

Instrumental line-profile-shape standards
Parrish, W., Wilson, A. J. C. and Langford, J. I.  International Tables for Crystallography (2006). Vol. C, Section 5.2.12, p. 501 [ doi:10.1107/97809553602060000596 ]
... Instrumental line-profile standards are required to determine resolution, as a check that alignment has been optimized, or to compare the ... therefore be required if samples of interest do not have a high absorption coefficient for the radiation used. In addition to ... by NIST as SRM 660 and it also serves as a line position standard. Other materials used as instrumental standards ...

Intensity standards
Parrish, W., Wilson, A. J. C. and Langford, J. I.  International Tables for Crystallography (2006). Vol. C, Section 5.2.11, p. 500 [ doi:10.1107/97809553602060000596 ]
... and CeO2. Table 5.2.11.1, taken from the NIST certificate, is a partial list of pertinent data. The lattice parameters have an ... of 3 parts in 105, which must be increased by a factor of 2 or 3 because of uncertainty in internal standards and thermal expansion. The five materials have a wide range of absorption coefficient and the crystallite size ( ...

Powder-diffraction standards
Parrish, W., Wilson, A. J. C. and Langford, J. I.  International Tables for Crystallography (2006). Vol. C, Section 5.2.10, pp. 498-499 [ doi:10.1107/97809553602060000596 ]
... and 95% of the particles are < 10µm. There is a wide range of particle sizes in SRM 640, and sieving ... to 298K. Because this wavelength was later found to have a systematic error (see Section 4.2.2 ), and a more accurate value, 1.5405929(5)Å (see Table 4.2.2.1 ), is ...

Testing for remanent systematic error
Parrish, W., Wilson, A. J. C. and Langford, J. I.  International Tables for Crystallography (2006). Vol. C, Section 5.2.9, p. 498 [ doi:10.1107/97809553602060000596 ]
... is lower. The IUCr lattice-parameter project (Parrish, 1960) showed a standard deviation of 1 in 30000 in inter-laboratory comparisons ... deviation of the sum S is expected to be approximately (Wilson, 1980), so that if the actual value of S exceeds ... remaining systematic error' based on likelihood were available; they assumed a normal distribution of errors, possibly without realizing, and certainly ...

Camera methods
Parrish, W., Wilson, A. J. C. and Langford, J. I.  International Tables for Crystallography (2006). Vol. C, Section 5.2.8, pp. 497-498 [ doi:10.1107/97809553602060000596 ]
... the apparent values of the lattice parameter were plotted against a function something like ([pi] - 2[theta])2. A function that has been found very satisfactory in practice was ... Jay arrangements. For Straumanis-Ievins', + or - and , respectively. References Langford, J. I., Pike, E. R. & Beu, K. E. (1964). ...

Energy-dispersive techniques
Parrish, W., Wilson, A. J. C. and Langford, J. I.  International Tables for Crystallography (2006). Vol. C, Section 5.2.7, pp. 496-497 [ doi:10.1107/97809553602060000596 ]
... available. In both, the specimen and detector are fixed in a selectable [theta]-2[theta] setting. The method (Giessen & Gordon, 1968) first described and most widely used requires a solid-state detector and a multichannel pulse-height analyser (Section 2.3.2 and Chapter 2.5 ) ...

Whole-pattern methods
Parrish, W., Wilson, A. J. C. and Langford, J. I.  International Tables for Crystallography (2006). Vol. C, Section 5.2.6, p. 496 [ doi:10.1107/97809553602060000596 ]
... Rietveld (1967, 1969) described in Chapter 8.6 . In outline, a profile-fitting function containing adjustable parameters to vary the width ... that is attained but the estimated standard deviations quoted in a number of papers (see, for example, Young, 1988) appear to ... are derived from profile fitting and the data used in a powder least-squares-refinement program. The reflections may be ...

Angle-dispersive diffractometer methods: synchrotron sources
Parrish, W., Wilson, A. J. C. and Langford, J. I.  International Tables for Crystallography (2006). Vol. C, Section 5.2.5, pp. 495-496 [ doi:10.1107/97809553602060000596 ]
... methods: synchrotron sources Lattice-parameter determination with synchrotron radiation has a number of advantages over focusing methods (Parrish, Hart, Huang & Bellotto ... low uniform background out to the highest [theta] values give a higher statistical counting precision, an important factor in accurate measurements. ... 2[theta]) when an analysing crystal is used instead of a receiving slit, and of the order of 0.05° when ...

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