Paul B. Klar- PhD in Physics
- Researcher at University of Bremen
Paul B. Klar
- PhD in Physics
- Researcher at University of Bremen
About
35
Publications
2,905
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238
Citations
Introduction
Electron crystallography
Current institution
Additional affiliations
March 2019 - September 2021
Position
- PostDoc Position
Description
- Electron Crystalloraphy Head of the Group: Lukas Palatinus
November 2014 - December 2018
Position
- PhD Student
Description
- "The Aperiodic Nature of Mullite" Supervisor: Gotzon Madariaga
May 2010 - August 2011
Publications
Publications (35)
Synchrotron single-crystal X-ray diffraction has revealed diffuse scattering alongside sharp satellite reflections for different samples of mullite (Al4+2xSi2−2xO10−x). Structural models have been developed in (3+1)-dimensional superspace that account for vacancy ordering and Al/Si ordering based on harmonic modulation functions. A constraint schem...
Continuous-rotation 3D electron diffraction methods are increasingly popular for the structure analysis of very small organic molecular crystals and crystalline inorganic materials. Dynamical diffraction effects cause non-linear deviations from kinematical intensities that present issues in structure analysis. Here, a method for structure analysis...
Estimating the error in the merged reflection intensities requires a full understanding of all the possible sources of error arising from the measurements. Most diffraction-spot integration methods focus mainly on errors arising from counting statistics for the estimation of uncertainties associated with the reflection intensities. This treatment m...
![Comparison of 3D-ΔPDF sections
3D-Δ\documentclass[12pt]{minimal}...](publication/374775137/figure/fig3/AS:11431281205335642@1700207712302/Comparison-of-3D-DPDF-sections-3D-Ddocumentclass12ptminimal-usepackageamsmath_Q320.jpg)
Structure-property relationships in ordered materials have long been a core principle in materials design. However, the introduction of disorder into materials provides structural flexibility and thus access to material properties that are not attainable in conventional, ordered materials. To understand disorder-property relationships, the disorder...
Detoxification of heme in Plasmodium depends on its crystallization into hemozoin. This pathway is a major target of antimalarial drugs. The crystalline structure of hemozoin was established by X-ray powder diffraction using a synthetic analog, β-hematin. Here, we apply emerging methods of in situ cryo-electron tomography and 3D electron diffractio...
Structure-property relationships in ordered materials have long been a core principle in materials design. However, the intentional introduction of disorder into materials provides structural flexibility and thus access to material properties that are not attainable in conventional, ordered materials. To understand disorder-property relationships,...
Detoxification of heme in Plasmodium and other blood-borne parasites results in crystallization of hemozoin. This crystallization is a major target of antimalarial drugs. The structure of hemozoin has been studied primarily by X-ray powder diffraction, which showed that the unit cell contains a centrosymmetric cyclic hematin dimer. The pro-chiral n...
Dynamical diffraction effects are usually considered a nuisance for structure analysis from continuous-rotation 3D electron diffraction (3D ED) data like cRED and MicroED. Here we demonstrate that by accounting for these effects during the structure refinement, significantly improved models can be obtained in terms of accuracy and reliability with...
Small‐pore zeolites such as chabazite (CHA) are excellent candidates for the selective separation of CO2; however, the current synthesis involves several steps and the use of organic structure‐directing agent (OSDA), increasing their cost and energy requirements. We report the synthesis of small‐pore zeolite crystals (aluminosilicate) with CHA‐type...
The synthesis of nanosized CHA‐type zeolite without organic structure‐directing agents is presented. The zeolite material exhibits excellent CO2 storage capacity, high stability under high‐temperature treatment, and selectivity towards CO2 over CH4, controlled by Cs⁺ in the host structure. The environmentally benign and energy‐efficient synthesis o...
3D Electron Diffraction for Structure Analysis of Challenging Inorganic Materials - Mariana Klementová, Lukas Palatinus, Paul Klar
The properties and crystal structure of two new polymorphs of [Fe(tvp)2(NCS)2] · tvp [tvp=trans-(4,4’-vinylenedipyridine)] are investigated. Despite being unusual in MOFs, one of them shows a commensurate modulation with q = (1 /4, 0, −1/4 ) at room temperature and an unmodulated triclinic structure at lower temperatures that requires a noticeable...
The benefit of computational methods applying density functional theory for the description and understanding of modulated crystal structures is investigated. A method is presented which allows one to establish, improve and test superspace models including displacive and occupational modulation functions from first-principles calculations on commen...
The average crystal structure of mullite (Al4+2xSi2-2xO10-x) is not easy to interpret in terms of the distribution of vacancies and Al/Si on the tetrahedral sites. Satellite reflections and diffuse scattering must be investigated to understand the ordering phenomena in the structure. From the reflection conditions of satellite reflections and the c...
A mullite single crystal with composition Al4.84Si1.16O9.58 (2) exhibiting sharp satellite reflections was investigated by means of X-ray diffraction. For the refinement of a superspace model in the superspace group Pbam(α0½)0ss different scale factors for main and satellite reflections were used in order to describe an ordered mullite structure em...
Questions
Question (1)
Dear scientists,
I (crystallographer) recently had a discussion with a colleague (chemist) about the ball-and-stick model about the meaning of a line/"stick" in graphical representations of crystal structures.
As we had quite different opinions, we started looking for an (official) definition or recommendations by journals/IUCr/IUPAC etc., but we only found definitions/recommendations concerning "Chemical Structure Diagrams".
1) Do you know if there is a resource providing recommendations that we have not found?
2) What is your idea of a line or stick in figures representing crystal structures?
3) Do you think a set of recommendations should be developed?
My personal opinion:
A stick/line does not represent a chemical bond, but it may indicate that linked atoms are bonded. It is rather an aid to the eye to help with the interpretation of the 2D projection in 3D so that one can easily see which atoms are "close" to each other and which atoms are not. The meaning of "close" of course depends on the atom type.
My colleague's opinion:
The ball-and-stick model is derived from the historic, chemical ball-and-stick model based on molecular modeling kits, in which the bond order is relevant for the choice of connection that is made between two balls. In his point of view many disciplines nowadays use the ball-and-stick concept, especially in 3D visualization programs, but neglect the original idea of the stick.
Currently everybody probably has a certain favorite program for the visualization of crystal structures (in my case: VESTA), and in some programs this original idea is maintained (e.g. Mercury) and different kinds of sticks are used to indicate single bonds, double bonds and H-bonds etc, whereas (I believe) the vast majority does not care about the meaning of the stick.
What do you think?
P.S.: Please mention if you consider yourself a chemist, physicist, crystallographer, biologist, mineralogist ...
