High precision measurement of Debye-Waller factors for NiAl

1995 ◽  
Vol 53 ◽  
pp. 140-141
Author(s):  
W. Niichter ◽  
A.L. Weickenmeier ◽  
J. Mayer
Keyword(s):  
Charge Density ◽  
Atomic Displacement ◽  
Waller Factor ◽  
Total Charge ◽  
High Precision Measurement ◽  
Atomic Vibrations ◽  
Total Charge Density ◽  
The Difference ◽  
Mott Formula ◽  
Image Position

Motivation Quantitative convergent beam electron diffraction (CBED) is increasingly appreciated as a tool to determine bonding charge densities of crystalline materials. Simulated CBED patterns are fitted to experimental ones to derive the structure factors. These are converted by means of the Mott formula to yield the total charge density. Finally a neutral atom total charge density is subtracted and the difference is interpreted as the bonding charge density. Accounting for the temperature by a Debye-Waller factor (DWF) the g-th Fourier coefficient of the bonding charge density is then given by where u denotes the thermal root mean square atomic displacement. Here we have assumed thesimplest case of identical isotropic atomic vibrations for all atoms in the crystal. In order to estimate the error in due to the uncertainty in u we insert the results obtained by Fox and Tabbernor for NiAl at room temperature. They found differences between atomic and measured values of in the order of 2 percent.

GAGs-Potentiated Inhibition of Thrombin, Factor Xa and Plasmin in Plasma and in a Purified System Containing Antithrombin III – Correlation with Total Charge Density

1981 ◽  
Vol 46 (04) ◽  
pp. 749-751 ◽  
Author(s):  
E Cofrancesco ◽  
A Vigo ◽  
E M Pogliani
Keyword(s):  
Charge Density ◽  
Chemical Structure ◽  
Antithrombin Iii ◽  
Factor Xa ◽  
Total Charge ◽  
Pure System ◽  
At Iii ◽  
Total Charge Density ◽  
The Difference ◽  
Inhibition Of Thrombin

SummaryThe ability of heparin and related glycosaminoglycans (GAGs) to accelerate the inhibition of thrombin, factor Xa and plasmin in plasma and in a purified system containing antithrombin III (At III) was studied using chromogenic peptide substrate assaysThere was a good correlation between the charge density of the mucopolysaccharides and the activities investigated. While the difference between potentiation of the antithrombin activity by GAGs in plasma and in the purified system was slight, the inhibition of factor Xa in plasma was more pronounced than in the presence of purified At III, indicating the mechanisms for GAGs-potentiated inhibition of thrombin and factor Xa are not identical.For the antiplasmin activity, there was a good correlation between the chemical structure and biological activity only in the pure system, confirming that the antithrombin-GAG complex plays a very limited role in the inactivation of plasmin in plasma.

Spin Density for Intermetallic Compounds

2018 ◽  
Vol 1 (1) ◽  
pp. 97-101
Author(s):  
Abeer E. Aly ◽  
D. P. Rai
Keyword(s):  
Charge Density ◽  
Spin Density ◽  
Pure Spin ◽  
Total Charge ◽  
Full Potential ◽  
Metal Compounds ◽  
Charge Densities ◽  
Spin Polarized ◽  
Density Map ◽  
The Difference

We first performed a pure spin-polarized calculation on Nd2Fe14B using the self-consistent Full Potential Linearized Augmented Plane Wave (FPLAPW). The total charge density and the spin density calculated by taking the sum or the difference of spin-up and spin-down charge densities, respectively. In this paper, we present the spin and charge density contours for rare-earth transition metal compounds e.g. Nd2Fe14B in the (001) and (110) planes using spin-polarized only. The charge density map and the spin density map on the (001) and (110) plane of the tetragonal cell show the evidence for covalent bonding between Fe and B atoms.

scholarly journals First-Principles Calculations on Atomic and Electronic Properties of Ge/4H-SiC Heterojunction

2018 ◽  
Vol 2018 ◽  
pp. 1-9
Author(s):  
Bei Xu ◽  
Changjun Zhu ◽  
Xiaomin He ◽  
Yuan Zang ◽  
Shenghuang Lin ◽  
...  
Keyword(s):  
Charge Density ◽  
Electronic Properties ◽  
Density Of States ◽  
First Principles ◽  
Density Functional ◽  
First Principles Calculation ◽  
Partial Density ◽  
Total Charge ◽  
Relaxation Energy ◽  
Total Charge Density

First-principles calculation is employed to investigate atomic and electronic properties of Ge/SiC heterojunction with different Ge orientations. Based on the density functional theory, the work of adhesion, relaxation energy, density of states, and total charge density are calculated. It is shown that Ge(110)/4H-SiC(0001) heterointerface possesses higher adhesion energy than that of Ge(111)/4H-SiC(0001) interface, and hence Ge/4H-SiC(0001) heterojunction with Ge[110] crystalline orientation exhibits more stable characteristics. The relaxation energy of Ge(110)/4H-SiC(0001) heterojunction interface is lower than that of Ge(111)/4H-SiC(0001) interface, indicating that Ge(110)/4H-SiC(0001) interface is easier to form at relative low temperature. The interfacial bonding is analysed using partial density of states and total charge density distribution, and the results show that the bonding is contributed by the Ge-Si bonding.

Effect of Molybdenum on the Electronic Structure of Iron Grain Boundaries with Phosphorus and Boron

1993 ◽  
Vol 319 ◽  
Author(s):  
Genrich L. Krasko
Keyword(s):  
Charge Density ◽  
Magnetic Moments ◽  
Method Comparison ◽  
Embedded Atom Method ◽  
Total Charge ◽  
Electron Charge Density ◽  
Density Distributions ◽  
Embedded Atom ◽  
Total Charge Density ◽  
Atomic Radii

AbstractWe are reporting preliminary results on LMTO supercell calculations on a Σ3 (111) grain boundary (GB) in Fe with Mo atoms sitting at the GB plane. Calculations were performed both for the clean (CL) GB and GB with P/B atoms occupying centers of host (Fe and Mo) atom trigonal prisms (a coordination typical of the Fe GBs). The geometry of the GBs was not changed upon substituting Mo for Fe in the GB plane: all the interplanar distances and atomic radii were preserved (these were calculated earlier for the Fe GBs from GB3 relaxation modelling using the Embedded Atom Method). Comparison of the electron charge-density distributions within the atomic spheres for GBs with and without Mo, has shown that the presence of Mo at the GB plane increases both the number of d-electrons and the total charge density within atomic spheres of the atoms most important for intergranular cohesion. This should result in enhanced cohesion. The magnetic moments of the constituent atoms were also found to be strongly affected by the addition of Mo. The Mo atoms are anti-ferromagnetically coupled with the neighboring Fe atoms: mM0=-O.6OμB (CL GB), mMo=-O.14μB (GB with P), and mMo=-O.18μB (GB with B).

Electronic wave functions round a vacancy in a metal

1960 ◽  
Vol 256 (1286) ◽  
pp. 400-415 ◽  
Keyword(s):  
Density Fluctuations ◽  
Wave Functions ◽  
Total Charge ◽  
Electronic Density ◽  
Thomas Fermi ◽  
Large Numbers ◽  
Self Consistent ◽  
Total Charge Density ◽  
The Difference ◽  
Number Of Particles

A calculation of the wave functions round a vacancy in a metal has been carried out for a simple model. This corresponds to the case of a finite number of particles in a free-electron metal, with the boundary condition that the wave functions vanish on the surface of the spherical metal. Calculations are reported for particle numbers of approximately 2 x 10 2 , 2 x 10 3 and 10 6 . The density fluctuations in the unperturbed metal are found to be serious for the first two cases, but by consideration of the difference between the electronic density distributions in the perturbed and the unperturbed cases, extrapolation from the case of a relatively small number of particles to obtain results valid for very large numbers is shown to be feasible in the region surrounding the vacancy. The possibility of obtaining an accurate density difference by consideration only of states of low orbital angular momentum is exploited. Comparison is made between the finite metal results, existing Thomas–Fermi calculations, and a self-consistent von Weizsäcker calculation which is also reported here. By examination of the solutions of Poisson’s equation, it is shown that the total charge density obtained by summing the squares of the normalized wave functions for the assumed Thomas–Fermi potential in the 10 6 particle case is such as to make this potential self-consistent to a good approximation. Our calculations also reveal long-range oscillations in the total perturbed electron density for finite metals. Although the amplitude of these oscillations decreases with increasing volume, extrapolation to the case of an infinite metal does not seem justified here. However, our calculations should provide an upper bound to the amplitude for the assumed potential, and the oscillations are small. Finally, brief reference is made to applications of the present results.

Sign in / Sign up

Export Citation Format

Share Document