Searching the crystal structure of silicon using the generalized scaled hypersphere search method with the rapid nuclear motion approximation

2020 ◽  
Vol 59 (3) ◽  
pp. 035503 ◽  
Author(s):  
Yuuki Midoro ◽  
Yoshitomo Kodaya ◽  
Hideo Yamakado ◽  
Koichi Ohno
Keyword(s):  
Crystal Structure ◽  
Search Method ◽  
Nuclear Motion ◽  
Motion Approximation

scholarly journals Stabilities and defect-mediated lithium-ion conduction in a ground state cubic Li3N structure

2016 ◽  
Vol 18 (5) ◽  
pp. 4185-4190 ◽  
Author(s):  
Manh Cuong Nguyen ◽  
Khang Hoang ◽  
Cai-Zhuang Wang ◽  
Kai-Ming Ho
Keyword(s):  
Crystal Structure ◽  
Ab Initio ◽  
Ground State ◽  
Lithium Ion ◽  
Search Method ◽  
Ground State Structure ◽  
State Structure ◽  
Cubic Symmetry ◽  
Structure Search ◽  
Lithium Ion Conduction

A stable ground state structure with cubic symmetry of Li3N (c-Li3N) is found by an ab initio initially symmetric random-generated crystal structure search method.

Structure predictions allowing more than one molecule in the asymmetric unit

2000 ◽  
Vol 56 (3) ◽  
pp. 535-542 ◽  
Author(s):  
Bouke P. van Eijck ◽  
Jan Kroon
Keyword(s):  
Crystal Structure ◽  
Structure Prediction ◽  
Random Search ◽  
Search Method ◽  
Hydroxyl Groups ◽  
Independent Molecule ◽  
Asymmetric Unit ◽  
Structure Generation ◽  
Independent Molecules ◽  
Experimental Structure

The UPACK program for crystal structure prediction was extended to allow the possibility of more than one molecule in the asymmetric unit. A search method was developed where the essential parameters (including torsional angles of hydroxyl groups) take random values. Energy minimization and clustering then lead to a list of hypothetical structures. In a test for six hexapyranoses this random search method was found to be approximately equally as efficient as the previously used systematic grid search method for one independent molecule. As a second test, the generation of structures with more than one independent molecule was performed for ethanol. A multitude of possible structures was found, the experimental one (two independent molecules in space group Pc) always being present. However, for \alpha-D-mannose (two independent molecules with five unknown hydroxyl torsional parameters each) the number of hypothetical structures was so large that the experimental structure was never encountered. Finally, a crystal structure generation for hydrates of pyranoses and polyalcohols was carried out. When the total number of unknown parameters was less than 20, the experimental structure was encountered. As usual, the empirical energies were not adequate to select that structure from the list of possible ones. Even then, the procedure proved to be valuable in identifying the most probable hydrogen-bonded network in cases where hydrogen positions in the experimental crystal structure were missing.

A structural study of polymorphism in phenyl salicylate: determination of the crystal structure of a meta-stable phase from X-ray powder diffraction data using a direct space systematic search method

2002 ◽  
Vol 217 (9) ◽  
Author(s):  
R. B. Hammond ◽  
M. J. Jones ◽  
K. J. Roberts ◽  
H. Kutzke ◽  
H. Klapper
Keyword(s):  
Crystal Structure ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Search Method ◽  
Systematic Search ◽  
Stable Phase ◽  
Powder Diffraction Data ◽  
Phenyl Salicylate ◽  
X Ray ◽  
Structure Solution

AbstractIn this paper we report the crystal structure solution of a meta-stable phase of phenyl salicylate (salol). This modification, which is obtained from a super-cooled melt, has been observed before, but the structure has not been previously determined. Structure solution was achieved by a procedure combining a computer based systematic search method with a subsequent Rietveld refinement of experimental X-ray powder diffraction data. A clustering procedure to group similar trial structures based upon energy minimisations is discussed. The best trial structure identified by the combination of a systematic search and clustering was refined using the Rietveld method and a final structure with a weighted pattern index

Crystal Structure Determination of Glycerol-Containing Lipids from Electron Diffraction Data. Use of Analog Compounds Based upon Configurational Isomers of Cyclopentane-1, 2, 3-TRIOL

1977 ◽  
Vol 35 ◽  
pp. 24-25
Author(s):  
Douglas L. Dorset ◽  
Anthony J. Hancock
Keyword(s):  
Crystal Structure ◽  
Electron Diffraction ◽  
Diffraction Data ◽  
Structure Determination ◽  
Crystal Surface ◽  
Coherent Scattering ◽  
Crystal Structure Determination ◽  
Electron Diffraction Data ◽  
Polar Group ◽  
Axis Orientation

Lipids containing long polymethylene chains were among the first compounds subjected to electron diffraction structure analysis. It was only recently realized, however, that various distortions of thin lipid microcrystal plates, e.g. bends, polar group and methyl end plane disorders, etc. (1-3), restrict coherent scattering to the methylene subcell alone, particularly if undistorted molecular layers have well-defined end planes. Thus, ab initio crystal structure determination on a given single uncharacterized natural lipid using electron diffraction data can only hope to identify the subcell packing and the chain axis orientation with respect to the crystal surface. In lipids based on glycerol, for example, conformations of long chains and polar groups about the C-C bonds of this moiety still would remain unknown.One possible means of surmounting this difficulty is to investigate structural analogs of the material of interest in conjunction with the natural compound itself. Suitable analogs to the glycerol lipids are compounds based on the three configurational isomers of cyclopentane-1,2,3-triol shown in Fig. 1, in which three rotameric forms of the natural glycerol derivatives are fixed by the ring structure (4-7).

Spherulitic crystal growth in the prodissoconch larval of Crassostrea virginica

1983 ◽  
Vol 41 ◽  
pp. 518-519
Author(s):  
George G. Cocks ◽  
Louis Leibovitz ◽  
DoSuk D. Lee
Keyword(s):  
Crystal Structure ◽  
Crassostrea Virginica ◽  
Crystal Orientation ◽  
Developmental Changes ◽  
Gastrula Stage ◽  
Orthorhombic Crystal ◽  
Orthorhombic Crystal Structure ◽  
Stages Of Growth ◽  
Early Stages ◽  
Initial Deposition

Our understanding of the structure and the formation of inorganic minerals in the bivalve shells has been considerably advanced by the use of electron microscope. However, very little is known about the ultrastructure of valves in the larval stage of the oysters. The present study examines the developmental changes which occur between the time of conception to the early stages of Dissoconch in the Crassostrea virginica(Gmelin), focusing on the initial deposition of inorganic crystals by the oysters.The spawning was induced by elevating the temperature of the seawater where the adult oysters were conditioned. The eggs and sperm were collected separately, then immediately mixed for the fertilizations to occur. Fertilized animals were kept in the incubator where various stages of development were stopped and observed. The detailed analysis of the early stages of growth showed that CaCO3 crystals(aragonite), with orthorhombic crystal structure, are deposited as early as gastrula stage(Figuresla-b). The next stage in development, the prodissoconch, revealed that the crystal orientation is in the form of spherulites.

Transmission Electron Microscopy studies of the vacancy ordering in YSI2-X thin films

1991 ◽  
Vol 49 ◽  
pp. 562-563
Author(s):  
F.-R. Chen ◽  
T. L. Lee ◽  
L. J. Chen
Keyword(s):  
Crystal Structure ◽  
Electron Microscopy ◽  
Thin Films ◽  
Diffraction Pattern ◽  
Annealing Temperature ◽  
Lattice Mismatch ◽  
Si Substrate ◽  
Metal Thin Films ◽  
Transmission Electron ◽  
Vacancy Ordering

YSi2-x thin films were grown by depositing the yttrium metal thin films on (111)Si substrate followed by a rapid thermal annealing (RTA) at 450 to 1100°C. The x value of the YSi2-x films ranges from 0 to 0.3. The (0001) plane of the YSi2-x films have an ideal zero lattice mismatch relative to (111)Si surface lattice. The YSi2 has the hexagonal AlB2 crystal structure. The orientation relationship with Si was determined from the diffraction pattern shown in figure 1(a) to be and . The diffraction pattern in figure 1(a) was taken from a specimen annealed at 500°C for 15 second. As the annealing temperature was increased to 600°C, superlattice diffraction spots appear at position as seen in figure 1(b) which may be due to vacancy ordering in the YSi2-x films. The ordered vacancies in YSi2-x form a mesh in Si plane suggested by a LEED experiment.

Crystal Structure Analysis of Cu-Zr Alloys by Convergent Beam Diffraction

1981 ◽  
Vol 39 ◽  
pp. 354-355
Author(s):  
A. F. Marshall ◽  
J. W. Steeds ◽  
D. Bouchet ◽  
S. L. Shinde ◽  
R. G. Walmsley
Keyword(s):  
Crystal Structure ◽  
Point Group ◽  
Intermetallic Phase ◽  
Three Dimensional ◽  
Crystal Structure Analysis ◽  
Ion Milling ◽  
Composition And Structure ◽  
Unit Cells ◽  
Sputter Deposited ◽  
Convergent Beam

Convergent beam electron diffraction is a powerful technique for determining the crystal structure of a material in TEM. In this paper we have applied it to the study of the intermetallic phases in the Cu-rich end of the Cu-Zr system. These phases are highly ordered. Their composition and structure has been previously studied by microprobe and x-ray diffraction with sometimes conflicting results.The crystalline phases were obtained by annealing amorphous sputter-deposited Cu-Zr. Specimens were thinned for TEM by ion milling and observed in a Philips EM 400. Due to the large unit cells involved, a small convergence angle of diffraction was used; however, the three-dimensional lattice and symmetry information of convergent beam microdiffraction patterns is still present. The results are as follows:1) 21 at% Zr in Cu: annealed at 500°C for 5 hours. An intermetallic phase, Cu3.6Zr (21.7% Zr), space group P6/m has been proposed near this composition (2). The major phase of our annealed material was hexagonal with a point group determined as 6/m.

High resolution STEM imaging study on high Tc superconductor YBa2CuaO7-x

1988 ◽  
Vol 46 ◽  
pp. 882-883
Author(s):  
H.-J. Ou ◽  
J. M. Cowley
Keyword(s):  
Crystal Structure ◽  
High Resolution ◽  
Grain Boundary ◽  
Strong Field ◽  
Imaging Study ◽  
Structure Defects ◽  
High Tc ◽  
High Tc Superconductor ◽  
Diffraction Patterns ◽  
Lattice Planes

Using the dedicate VG-HB5 STEM microscope, the crystal structure of high Tc superconductor of YBa2Cu3O7-x has been studied via high resolution STEM (HRSTEM) imaging and nanobeam (∽3A) diffraction patterns. Figure 1(a) and 2(a) illustrate the HRSTEM image taken at 10' times magnification along [001] direction and [100] direction, respectively. In figure 1(a), a grain boundary with strong field contrast is seen between two crystal regions A and B. The grain boundary appears to be parallel to a (110) plane, although it is not possible to determine [100] and [001] axes as it is in other regions which contain twin planes [3]. Following the horizontal lattice lines, from left to right across the grain boundary, a lattice bending of ∽4° is noticed. Three extra lattice planes, indicated by arrows, were found to terminate at the grain boundary and form dislocations. It is believed that due to different chemical composition, such structure defects occur during crystal growth. No bending is observed along the vertical lattice lines.

Crystal structure images of large gold clusters and growing crystals by HRTEM

1984 ◽  
Vol 42 ◽  
pp. 428-429
Author(s):  
L.R. Wallenberg ◽  
J.-O. Bovin ◽  
G. Schmid
Keyword(s):  
Crystal Structure ◽  
Nucleation And Growth ◽  
Close Packing ◽  
Gold Clusters ◽  
Molecular Weight Determination ◽  
Growth Mechanisms ◽  
Starting Point ◽  
Different Types ◽  
Nucleation And Growth Mechanisms ◽  
Points Of View

Metallic clusters are interesting from various points of view, e.g. as a mean of spreading expensive catalysts on a support, or following heterogeneous and homogeneous catalytic events. It is also possible to study nucleation and growth mechanisms for crystals with the cluster as known starting point.Gold-clusters containing 55 atoms were manufactured by reducing (C6H5)3PAuCl with B2H6 in benzene. The chemical composition was found to be Au9.2[P(C6H5)3]2Cl. Molecular-weight determination by means of an ultracentrifuge gave the formula Au55[P(C6H5)3]Cl6 A model was proposed from Mössbauer spectra by Schmid et al. with cubic close-packing of the 55 gold atoms in a cubeoctahedron as shown in Fig 1. The cluster is almost completely isolated from the surroundings by the twelve triphenylphosphane groups situated in each corner, and the chlorine atoms on the centre of the 3x3 square surfaces. This gives four groups of gold atoms, depending on the different types of surrounding.

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