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Refinement of the λ/2 contribution to CCD detector data
Author(s) -
Dudka Alexander
Publication year - 2010
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889809051577
Subject(s) - wavelength , diffractometer , detector , optics , displacement (psychology) , physics , computational physics , scattering , charge density , reflection (computer programming) , computer science , scanning electron microscope , psychology , quantum mechanics , psychotherapist , programming language
A new method is proposed to improve structure modeling by taking into account the half‐wavelength contribution (λ/2) to X‐ray data measured on CCD and image‐plate diffractometers. Such an effect arises because the reflection intensities contain contributions associated with both the λ and the λ/2 wavelengths. The ratio w of these two contributions is a new parameter refined using the full‐matrix least‐squares techniques. The new method does not require any additional measurement or information. According to the tests performed, proper account of the λ/2 contribution lowers the wR 2 (| F | 2 ) factors by a relative percent difference of 4–14% and the atomic displacement parameters by ∼1–4 s.u. Other effects are analyzed that might correlate with the λ/2 contribution, such as absorption, charge‐density redistribution, thermal diffuse scattering and extinction. Strong correlation was found between w and the other parameters, but a fixed λ/2 correction reduces this difficulty. The value of w is found to be both characteristic of the diffractometer and a general indicator of the refinement quality (similar to R factors).