Crystal structures of laihunite and intermediate phases between laihunite-1M and fayalite: Z-contrast imaging and ab initio study

2014 ◽  
Vol 99 (5-6) ◽  
pp. 881-889 ◽  
Author(s):  
H. Xu ◽  
Z. Shen ◽  
H. Konishi ◽  
P. Fu ◽  
I. Szlufarska
Keyword(s):  
Ab Initio ◽  
Crystal Structures ◽  
Ab Initio Study ◽  
Contrast Imaging ◽  
Intermediate Phases ◽  
Z Contrast

scholarly journals Z-contrast imaging and ab initio study on "d" superstructure in sedimentary dolomite

2014 ◽  
Vol 99 (7) ◽  
pp. 1413-1419 ◽  
Author(s):  
Z. Shen ◽  
H. Konishi ◽  
I. Szlufarska ◽  
P. E. Brown ◽  
H. Xu
Keyword(s):  
Ab Initio ◽  
Ab Initio Study ◽  
Contrast Imaging ◽  
Z Contrast

scholarly journals Ab initio study of elastic anisotropies and thermal conductivities of rhenium diborides in different crystal structures

RSC Advances ◽  
2020 ◽  
Vol 10 (61) ◽  
pp. 37142-37152
Author(s):  
Yi X. Wang ◽  
Ying Y. Liu ◽  
Zheng X. Yan ◽  
W. Liu ◽  
Jian B. Gu
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Crystal Structures ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Ab Initio Study ◽  
Ambient Conditions ◽  
Functional Theory ◽  
Thermal Conductivities

The phase stabilities, elastic anisotropies, and thermal conductivities of ReB2 diborides under ambient conditions have been investigated by using density functional theory calculations.

Crystal chemistry of tetraradial species. Part 3. Salts of aliphatic Schiff bases crystallizable from aqueous media: crystal structures of five iminium tetraphenylborates and a 6-31G* ab initio study of simple iminium ions

1993 ◽  
Vol 71 (9) ◽  
pp. 1495-1523 ◽  
Author(s):  
Osvald Knop ◽  
T. Stanley Cameron ◽  
Pradip K. Bakshi ◽  
Witold Kwiatkowski ◽  
S.C. Choi ◽  
...  
Keyword(s):  
Ab Initio ◽  
Bond Length ◽  
Crystal Structures ◽  
Schiff Bases ◽  
Linear Functions ◽  
Planar Geometry ◽  
Ab Initio Study ◽  
Complete Replacement ◽  
Iminium Ions ◽  
Length Range

Recrystallization of a primary or secondary alkylammonium tetraphenylborate (TB) from approximately 1:1 mixtures of Me2CO (or MeEtCO) and water yields, against expectation, the TB of the corresponding iminium cation and thus provides an easy route to a variety of aliphatic Schiff bases. The crystal structures of five such salts have been determined: A, [Me2C = NHMe]BPh4 (Cmcm, a = 10.747(2) Å, b = 15.641(4) Å, c = 13.453(4) Å, Z = 4); B, [Me2,C = NMe2,]BPh4 (Cmca, a = 13.196(4) Å, b = 14.469(3) Å, c = 25.122(4) Å. Z = 8); C, [Me,C = NHEt]BPh4 (P21/n, a = 12.146(3) Å, b = 14.099(2) Å, c = 14.177(3) Å, β = 96.23(2)°, Z = 4); D, [MeEtC=NHMe]BPh4 (Cmc21, a = 10.967(5) Å, b = 15.642(5) Å, c = 13.430(4) Å, Z = 4); E, [Me2C=NH(β-CH2CH2Ph)]BPh4 H2O (C2/c, a = 30.747 Å, b = 9.845(4) Å, c = 19.741(5) Å, β = 97.12(2)°, Z = 8). The building principles of these and related TBs are discussed in detail, as also is the tendency of the small iminium ions to orientational disorder. The range of the C=N bond length in these and other iminium salts is quite narrow, with 1.283(12) Å as the mean (uncorrected) value. Where a hydrogen atom(s) is attached to the iminium nitrogen, it will form a hydrogen bond (simple or bifurcated) with the aromatic π system of the nearest phenyl ring(s). The narrowness of the C=N bond-length range with respect to substitution on the cation has prompted a detailed 6-31G* ab initio study of the effect, on the geometry of the [H2C=NH2]+ ion, of a partial or complete replacement of the H atoms by one of the following substituents: F, Cl, CN, Li, and Na. The 46 structures optimized in planar geometry were supplemented by a number of optimizations of similarly substituted ethylenes as well as by a few optimizations in perpendicular geometry. Analysis of the numerical results involves the bond lengths and angles, Mulliken εM and (in part) Löwdin εL net charges on the atoms, and electron densities ρc = ρ(rc) at the bond critical points. Only a limited use has been made of comparisons involving the total electronic energies E (substitutional isomerism). Since the above substituents span the entire electronegativity scale, and CN provides for the possibility of conjugation, the effects they produce are expected to bracket the effects that would be produced by any other substituents. The calculations confirm the essential narrowness of the C=N bond-length range in iminium ions. They also show that, at least in the 6-31G* scheme, the nitrogen in [H2C=NH2]+ carries a significant negative net charge (both in terms of εM and εL), which is contrary to the conventional representation of the ion as H2C=N+H2. The trends observed in the parameters are smooth and highly self-consistent except for the tri- and tetrasubstituted ions containing Li or Na, where interligand repulsions may invalidate the assumption of planarity. Many of the parameters can be represented to a high degree of correlation as linear functions α0 + αCnC(X) + αNnN(X) of the numbers n of substituent atoms X on the C and N atoms. This representation makes it possible to estimate the contribution to the parameter value from the substitution at the distant atom of the C=N bond, i.e., the extent of localization of the effect produced by the substituent. The success of the linearization of the parameter variation raises the important question of whether the apparent additivity is genuine and intrinsic or merely a property of the 6-31G* optimization scheme. In other words, will additivity be retained, functionally, for sets of parameters obtained from higher level ab initio calculations, and will it be eventually verified by experiment?

scholarly journals Direct retrieval of crystal structures by maximum-entropy analysis of incoherent Z-contrast images

1994 ◽  
Vol 52 ◽  
pp. 916-917
Author(s):  
A. J. McGibbon ◽  
S. J. Pennycook
Keyword(s):  
Image Processing ◽  
Maximum Entropy ◽  
Crystal Structures ◽  
Electron Probe ◽  
Current Density Distribution ◽  
Incident Electron ◽  
Image Processing Technique ◽  
Bayesian Probability ◽  
Contrast Imaging ◽  
Z Contrast

Z-contrast imaging of crystalline specimens in a scanning transmission electron microscope (STEM) can provide directly interpretable images of crystal structures at atomic resolution with strong compositional sensitivity. The key feature of the technique is that, by recording images using high-anglethermally diffuse scattered electrons, the resultant image is incoherent, and can be interpreted as aconvolution between the incident electron probe and the projected crystal structure of the specimen. Consequently, the technique is ideally suited to the application of deconvolution routines which enable the retrieval of the original crystal lattice by means of an incident electron probe approximation, and with no prior assumption of the nature of the crystal itself. Here, we show that by applying the image processing technique of maximum entropy, such a retrieval can be achieved with high accuracy,enhancing spatial resolution whilst preserving Z-sensitivity.Maximum entropy is an image processing routine based on Bayesian probability which produces a ‘most likely’ reconstruction of the original image given a particular point spread function, or in this case, electron probe current density distribution.

Crystal structures of curium compounds: an ab initio study

2003 ◽  
Vol 322 (2-3) ◽  
pp. 165-179 ◽  
Author(s):  
V Milman ◽  
B Winkler ◽  
C.J Pickard
Keyword(s):  
Ab Initio ◽  
Crystal Structures ◽  
Ab Initio Study

Ab Initio Study of the Sodium Intercalation and Intermediate Phases in Na0.44MnO2 for Sodium-Ion Battery

2012 ◽  
Vol 24 (6) ◽  
pp. 1205-1211 ◽  
Author(s):  
Heejin Kim ◽  
Dong Jun Kim ◽  
Dong-Hwa Seo ◽  
Min Sun Yeom ◽  
Kisuk Kang ◽  
...  
Keyword(s):  
Ab Initio ◽  
Sodium Ion ◽  
Sodium Ion Battery ◽  
Ab Initio Study ◽  
Intermediate Phases
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