Accuracy of a random-walk-based approach in the determination of equilibrium bond lengths and harmonic frequencies for some doublet first-row diatomic radicals

2005 ◽  
Vol 123 (7) ◽  
pp. 074104
Author(s):  
Shih-I Lu
Keyword(s):  
Random Walk ◽  
Bond Lengths ◽  
Harmonic Frequencies

Determination of bond lengths in some compounds of rhenium from the x-ray LIII absorption discontinuity

Pramana ◽  
1973 ◽  
Vol 1 (2) ◽  
pp. 104-108 ◽  
Author(s):  
A V Pendharkar ◽  
Chintamani Mande
Keyword(s):  
X Ray ◽  
Bond Lengths

Accuracy of the final model

2002 ◽  
Author(s):  
David Blow
Keyword(s):  
Data Bank ◽  
The Other ◽  
Protein Crystal ◽  
Major Error ◽  
Final Model ◽  
Bond Angles ◽  
Bond Lengths ◽  
R Factor ◽  
Insight Into

The result of all the work described in the previous chapters will be a set of coordinates and other data suitable for deposit in the Protein Data Bank. You or I may use these coordinates, and we need to have some insight into their accuracy and reliability. In the previous chapters, indicators have been described, which may suggest aspects of the data or interpretation procedures that might lead to problems. But as the determination of protein crystal structures becomes more routine, many of these indicators are omitted from publications. Fortunately, crystallographic procedures are self-checking to a large extent. It is rare for a major error of interpretation to lead right through to a published refined structure. A high Rfree factor is a warning, especially if coupled with departures from the requirements of correct bond lengths, angles, and acceptable dihedral angles. On the other hand, there will always be a desire to squeeze more results from the data. All interpretations are subject to error; nearly all protein crystals have regions that are less ordered, where accurate interpretation is less feasible; and the structure may be overrefined, using too many variables for the data. If the majority of the molecule is correctly interpreted, a reasonable R factor may be obtained even though some small regions are completely wrong. During refinement it is usual to restrain the bond lengths and bond angles to be near their theoretical values, as described in Chapter 12. The extent to which bond lengths and bond angles depart from these values is often quoted as an indicator of accuracy. These departures are, however, difficult to interpret because they depend on how tightly the restraints have been applied. The same applies to the restraint of certain coordinates to lie in a plane. This difficulty illustrates a general problem. Designers of refinement procedures are understandably anxious to improve their procedures to lead directly to a well-refined structure. Every aspect of structure that can be recognized as having a regularity could, in principle, be expressed as a restraint which enforces it during refinement.

Intraionic Structure of HS04- and Alkali Cation Configuration in Molten NaHS04 and KHS04

1994 ◽  
Vol 49 (7-8) ◽  
pp. 785-789 ◽  
Author(s):  
K. Fukushima ◽  
M. Murofushi ◽  
M . Oki ◽  
K. Igarashi ◽  
J. Mochinaga ◽  
...  
Keyword(s):  
Molten Salts ◽  
Molecular Orbital Calculations ◽  
Distorted Tetrahedron ◽  
X Ray Diffraction ◽  
X Ray ◽  
Bond Lengths ◽  
Semi Empirical ◽  
Polyatomic Anion ◽  
Short Range Structure

Abstract The short range structure of molten NaHSO4(I) and KHSO4(II) was estimated by X-ray diffraction. The polyatomic anion, HSO4-, in both molten salts was found to have a distorted tetrahedral structure in which the bond lengths of S-O and S-OH were 1.45 Å and 1.53 Å in (I) and 1.46 Å and 1.56 Å in (II), respectively. The coordination number of the Na+ or K+ around the HSO4- was evaluated to be about unity. The semi-empirical molecular orbital calculations by the MNDO-MOPAC method were applied to the determination of the intraionic structure of the H S 0 4 and the bond lengths of S-O and S -OH were computed to be 1.528 Å and 1.666 Å, respectively, supporting qualitatively that the HSO4- forms a rather distorted tetrahedron.

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