Equivalent isotropic displacement parameters

Table 2 Atomic coordinates and equivalent isotropic displacement parameters (Angstroms2) l for [ Cu(im idazole) ClJCl, Ueq is defined as one third of the trace of the orthogonalized lfJ tensor.

Equivalent isotropic displacement parameters An expression representing the extent of thermal displacement of an atom, averaged over all directions ... 

The isotropic B-value that is commonly used in macromolecular crystallography is related to tiie equivalent isotropic displacement parameter U q by the equation Biso = t/eq. A guide to the different nomenclatures used to... 

Table A.8 Atomic coordinates (xlO" ) and equivalent isotropic displacement parameters...

Atoms in crystals seldom have isotropic environments, and a better approximation (but still an approximation) is to describe the atomic motion in terms of an ellipsoid, with larger amplitudes of vibration in some directions than in others. Six parameters, the anisotropic vibration or displacement parameters, are introduced for each atom. Three of these parameters per atom give the orientations of the principal axes of the ellipsoid with respect to the unit cell axes. One of these principal axes is the direction of maximum displacement and the other two are perpendicular to this and also to each other. The other three parameters per atom represent the amounts of displacement along these three ellipsoidal axes. Some equations used to express anisotropic displacement parameters, which may be reported as 71, Uij, or jdjj, axe listed in Table 13.1. Most crystal structure determinations of all but the largest molecules include anisotropic temperature parameters for all atoms, except hydrogen, in the least-squares refinement. Usually, for brevity, the equivalent isotropic displacement factor Ueq, is published. This is expressed as ... 

O positional parameters and isotropic or equivalent displacement parameters O bond distances, angles, and torsion angles ... 

Note-. Cubic space group Pniim (No. 221). Number of formula units of Lao,6Sro.4Co03 in a unit cell Z= 1. Unit-cell parameters a = b = c = 3.9496 (3) A, a = P = y = 90° unit-cell volume 61.612(9) A g, occupancy x, y, z, fractional coordinates U, isotropic atomic displacement parameters equivalent isotropic atomic displacement parameters anisotropic atomic displa-... 

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