Entity

Time filter

Source Type

Hong Kong, Hong Kong

Yuen P.S.,237 Des Voeux Road West
Zeitschrift fur Kristallographie - Crystalline Materials | Year: 2015

Besides the commonly employed refinement by minimization of the R factor, there is refinement by atomicity. These two refinements lead to two refined structures. Both structures are reasonable and close to each other. The differences between the results of these two refinements are significant. Refinement by atomicity is used as a supplement to refinement by minimization of R factor. For any crystal structure determined by minimization of R factor or other method, with all atoms determined and occupancy of each site equal to 1, in principle, refinement by atomicity should be applied. The purpose is to improve the atomic coordinates. It remains for the X-ray crystallographers to devise a procedure to obtain an improved structure from these two refined structures. The procedure can then be applied to all crystal structures reported in the literatures, or will be published in the future. This means that most articles in X-ray crystallography need to be improved. Many articles and books in other disciplines directly or indirectly contain or use structural informations, such as bond lengths and bond angles, obtained in X-ray crystallography. All these articles and books need to be revised. Source


The binary object treated is a square with a square hole. We first use a set of initial phases to determine the symmetry of the object. The initial image has the gross shape of a square with a square hole, and preserves symmetry of the object. With another set of initial phases, the initial image has gross shape of a square with a hole. Sayre's equation is applied to refine this gross shape. After iterations, the result shows a square with a distorted square hole. These three squares have approximately same edge lengths. These squares are larger than the object. The holes are smaller than the hole of the object. The initial phases or the gross shapes can be used as starting phases or starting envelopes in other iterative algorithms. © 2014 Elsevier GmbH. All rights reserved. Source


The binary object treated is a square. We first use a set of initial phases to determine the symmetry of the object. The result shows a well-shaped image, and preserves symmetry of the object. We then use another set of initial phases. The result has gross shape of a square with approximately correct dimensions. Sayre's equation is applied to refine the gross shape. After iterations, the result shows an image which is close to a square with sharp boundary and has approximately correct dimensions. The charge densities of the image are approximately evenly distributed, scattering about the value of 1, and has no negative charge density. The shape of the binary object is obtained. The initial phases or the gross shape can be used as starting phases or starting envelope in other iterative algorithms. © 2014 Elsevier GmbH. All rights reserved. Source


Yuen P.S.,237 Des Voeux Road West
Optik | Year: 2014

Using unit cell of smaller edge lengths to calculate the initial phases can reduce the size of the initial image. © 2014 Elsevier GmbH. All rights reserved. Source

Discover hidden collaborations