scholarly journals Experimental core electron density of cubic boron nitride

2014 ◽  
Vol 70 (a1) ◽  
pp. C283-C283
Author(s):  
Nanna Wahlberg ◽  
Niels Bindzus ◽  
Lasse Bjerg ◽  
Jacob Becker ◽  
Bo Iversen
Keyword(s):  
Boron Nitride ◽  
Charge Density ◽  
Electron Density ◽  
Cubic Boron Nitride ◽  
Experimental Result ◽  
Total Density ◽  
Strongly Correlated ◽  
Core Density ◽  
Core Electron ◽  
The Core

The resent progress in powder diffraction provides data of quality beyond multipolar modeling of the valence density. As was recently shown in a benchmark study of diamond by Bindzus et al.[1] The next step is to investigate more complicated chemical bonding motives, to determine the effect of bonding on the core density. Cubic boron nitride lends itself as a perfect candidate because of its many similarities with diamond: bonding pattern in the extended network structure, hardness, and the quality of the crystallites.[2] However, some degree ionic interaction is a part of the bonding in boron nitride, which is not present in diamond. By investigating the core density in boron nitride we may obtain a deeper understanding of the effect of bonding on the total density. We report here a thorough investigation of the charge density of cubic boron nitride with a detailed modelling of the inner atom charge density. By combining high resolution powder X-ray diffraction data and an extended multipolar model an experimental modeling of the core density is possible.[3] The thermal motion is a problem since it is strongly correlated to the changes of the core density, but by combining the average displacement from a Wilson plot and a constrained refinement, a reasonable result has been obtained. The displacement parameters reported here are significantly lower than those previously reported, stressing the importance of an adequate description of the core density. The charge transfer from boron to nitrogen clearly affects the inner electron density, which is evident from theoretical as well as experimental result. The redistribution of electron density will, if not accounted for, result in increased thermal parameters. It is estimated that 1.7-2 electrons is transferred from boron to nitrogen.

Ab initio Hartree–Fock study of the electronic charge density of the cubic boron nitride and its comparison with experiments

1996 ◽  
Vol 52 (4) ◽  
pp. 586-595 ◽  
Author(s):  
A. Lichanot ◽  
P. Azavant ◽  
U. Pietsch
Keyword(s):  
Charge Transfer ◽  
Boron Nitride ◽  
Charge Density ◽  
Ab Initio ◽  
Cubic Boron Nitride ◽  
Electronic Charge ◽  
Total Density ◽  
Electronic Charge Density ◽  
Acta Cryst ◽  
Hartree Fock

The electronic charge density of cubic boron nitride is calculated within the ab initio Hartree–Fock approximation using the program CRYSTAL. Based on Debye hypothesis, the thermal motion of atoms is considered by disturbing the atomic orbitals by mean-square displacements given from experiment. The calculated difference charge density obtained by subtraction of the total density and that of an independent atomic model (IAM) is characterized by a charge-density accumulation between next neighbours slightly shifted towards the nitrogen. The calculated X-ray structure amplitudes are compared with two different data sets [Josten (1985). Thesis. University of Bonn, Germany; Eichhorn, Kirfel, Grochowski & Serda (1991). Acta Cryst. B47, 843–848]. In both cases, very good agreement is found beyond the 420 reflection. The first six structure amplitudes are generally lower or larger compared with Josten's and Eichhorn et al.'s data, respectively. Whereas our charge density can be interpreted by a balanced ratio between covalent overlap and electronic charge transfer between neighbouring valence shells, the density plots calculated from experimental data express either the charge transfer (Josten, 1985) or the covalency (Eichorn et al., 1991).

Electron Density Studies of Molecular Crystals

1997 ◽  
Author(s):  
Philip Coppens
Keyword(s):  
Charge Density ◽  
Electron Scattering ◽  
Experimental Studies ◽  
Molecular Crystals ◽  
Chemical Environment ◽  
Light Atom ◽  
Core Electron ◽  
The Core ◽  
Core Electrons ◽  
Electron Donor And Acceptor

Small molecules consisting of light-, few-electron atoms were the first species beyond atoms to yield to quantum-mechanical methods. Similarly, crystals of small light-atom molecules have served as most useful test cases of charge density mapping. The small number of core electrons in first-row atoms enhances the relative contribution of valence electron scattering to the diffraction pattern. Early studies, done just after automated diffractometers became widely available, were concerned with molecular crystals such as uracil (Stewart and Jensen 1967), s-triazine (Coppens 1967), oxalic acid dihydrate (Coppens et al. 1969), decaborane (Dietrich and Scheringer 1978), fumaramic acid (Hirshfeld 1971), glycine (Almlof et al. 1973), and tetraphenylbutatriene (Berkovitch-Yellin and Leiserowitz 1976). While thermal motion is often pronounced in molecular crystals, advances in low-temperature data collection have done much to alleviate this disadvantage. In recent years, subliquid-nitrogen cooling techniques have been increasingly applied. Among the most interesting aspects of molecular crystals are the influence of intermolecular interactions on the electronic structure. Physically meaningful Coulombic parameters pertinent to a molecule in a condensed environment can be obtained from the diffraction analysis, and can be used in the modeling of macromolecules. The enhancement of the electrostatic moments relative to those of the isolated species has been noted in chapter 7. But, beyond these considerations, molecular crystals are important in their own right. For example, crystals of aromatic molecules substituted with π-electron donor and acceptor groups are among the most strongly nonlinear optical solids known, considerably exceeding the nonlinearity of inorganic crystals such as potassium titanyl phosphate (KTP); while mixed-valence organic components of low-dimensional solids can become superconducting at low temperatures. The relation between such properties of molecular crystals and their charge distribution provides a continuing impetus for further study. The suitability of light-atom crystals for charge density analysis can be understood in terms of the relative importance of core electron scattering. As the perturbation of the core electrons by the chemical environment is beyond the reach of practically all experimental studies, the frozen-core approximation is routinely used. It assumes the intensity of the core electron scattering to be invariable, while the valence scattering is affected by the chemical environment, as discussed in chapter 3.

Charge density and chemical bonding in cubic boron nitride

1986 ◽  
Vol 117 (1-2) ◽  
pp. 61-71 ◽  
Author(s):  
G. Will ◽  
A. Kirfel ◽  
B. Josten
Keyword(s):  
Boron Nitride ◽  
Charge Density ◽  
Chemical Bonding ◽  
Cubic Boron Nitride

scholarly journals Tailoring the core electron density in modulation-doped core−multi-shell nanowires

2016 ◽  
Vol 27 (19) ◽  
pp. 195201 ◽  
Author(s):  
Fabrizio Buscemi ◽  
Miquel Royo ◽  
Guido Goldoni ◽  
Andrea Bertoni
Keyword(s):  
Electron Density ◽  
Core Electron ◽  
The Core ◽  
Shell Nanowires

Powder X-ray Diffraction Electron Density of Cubic Boron Nitride

2015 ◽  
Vol 119 (11) ◽  
pp. 6164-6173 ◽  
Author(s):  
Nanna Wahlberg ◽  
Niels Bindzus ◽  
Lasse Bjerg ◽  
Jacob Becker ◽  
Sebastian Christensen ◽  
...  
Keyword(s):  
Boron Nitride ◽  
Electron Density ◽  
Cubic Boron Nitride ◽  
X Ray Diffraction ◽  
X Ray ◽  
Diffraction Electron

Structural relationships in the synthesis of cubic boron nitride thin films by ion-assisted deposition

1994 ◽  
Vol 52 ◽  
pp. 638-639
Author(s):  
D. L. Medlin ◽  
T. A. Friedmann ◽  
P. B. Mirkarimi ◽  
M. J. Mills ◽  
K. F. McCarty
Keyword(s):  
Boron Nitride ◽  
Ion Irradiation ◽  
Cubic Boron Nitride ◽  
Film Stress ◽  
Bonded Phases ◽  
Structural Relationships ◽  
Precursor Material ◽  
Pressure Synthesis ◽  
Microstructure Of The Material

The allotropes of boron nitride include two sp2-bonded phases with hexagonal and rhombohedral structures (hBN and rBN) and two sp3-bonded phases with cubic (zincblende) and hexagonal (wurtzitic) structures (cBN and wBN) (Fig. 1). Although cBN is synthesized in bulk form by conversion of hBN at high temperatures and pressures, low-pressure synthesis of cBN as a thin film is more difficult and succeeds only when the growing film is simultaneously irradiated with a high flux of ions. Only sp2-bonded material, which generally has a disordered, turbostratic microstructure (tBN), will form in the absence of ion-irradiation. The mechanistic role of the irradiation is not well understood, but recent work suggests that ion-induced compressive film stress may induce the transformation to cBN.Typically, BN films are deposited at temperatures less than 1000°C, a regime for which the structure of the sp2-bonded precursor material dictates the phase and microstructure of the material that forms from conventional (bulk) high pressure treatment.

Cambiarenes: Single-Step Synthesis and Anion Binding of a Clip- Shaped Macrocycle with a Redox-Active Core

2019 ◽  
Author(s):  
Riley J. Petersen ◽  
Brett J. Rozeboom ◽  
Shalisa Oburn ◽  
Nolan Blythe ◽  
Tanner Rathje ◽  
...  
Keyword(s):  
Electron Density ◽  
Single Step ◽  
Anion Binding ◽  
Host Molecule ◽  
Selective Binding ◽  
The Core ◽  
Redox Active ◽  
Active Core ◽  
Guest Binding

<div>We report the synthesis of a novel macrocyclic host molecule that forms in a single step from commercially available starting materials. The core of the macrocycle backbone possesses two quinone rings and, thus, is redox-active. Host-guest binding involving the clip-shaped cavity indicates selective binding of pyridine <i>N</i>-oxides based of the electron density of and steric bulk of the anionic oxygen.</div>

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