scholarly journals Visualizing atomic sizes and molecular shapes with the classical turning surface of the Kohn–Sham potential

2018 ◽  
Vol 115 (50) ◽  
pp. E11578-E11585 ◽  
Author(s):  
Egor Ospadov ◽  
Jianmin Tao ◽  
Viktor N. Staroverov ◽  
John P. Perdew
Keyword(s):  
Covalent Bond ◽  
State Density ◽  
Orbital Energy ◽  
Pictorial Representation ◽  
Ionic Radii ◽  
Molecular Surfaces ◽  
Atomic Ions ◽  
Empirical Estimates ◽  
Multiplicative Operator ◽  
Chemical Trends

The Kohn–Sham potential veff(r) is the effective multiplicative operator in a noninteracting Schrödinger equation that reproduces the ground-state density of a real (interacting) system. The sizes and shapes of atoms, molecules, and solids can be defined in terms of Kohn–Sham potentials in a nonarbitrary way that accords with chemical intuition and can be implemented efficiently, permitting a natural pictorial representation for chemistry and condensed-matter physics. Let ϵmax be the maximum occupied orbital energy of the noninteracting electrons. Then the equation veff(r)=ϵmax defines the surface at which classical electrons with energy ϵ≤ϵmax would be turned back and thus determines the surface of any electronic object. Atomic and ionic radii defined in this manner agree well with empirical estimates, show regular chemical trends, and allow one to identify the type of chemical bonding between two given atoms by comparing the actual internuclear distance to the sum of atomic radii. The molecular surfaces can be fused (for a covalent bond), seamed (ionic bond), necked (hydrogen bond), or divided (van der Waals bond). This contribution extends the pioneering work of Z.-Z. Yang et al. [Yang ZZ, Davidson ER (1997) Int J Quantum Chem 62:47–53; Zhao DX, et al. (2018) Mol Phys 116:969–977] by our consideration of the Kohn–Sham potential, protomolecules, doubly negative atomic ions, a bond-type parameter, seamed and necked molecular surfaces, and a more extensive table of atomic and ionic radii that are fully consistent with expected periodic trends.

First-Principles Studies on Electronic Structures of ZnO

2014 ◽  
Vol 926-930 ◽  
pp. 444-447
Author(s):  
Fu Chun Zhang ◽  
Xian Hui Zhong ◽  
Xing Xiang Ruan ◽  
Wei Hu Zhang
Keyword(s):  
Electronic Structure ◽  
Valence Band ◽  
Conduction Band ◽  
Density Functional ◽  
Covalent Bond ◽  
Potential Method ◽  
State Density ◽  
Conduction Band Bottom ◽  
Oxide Semiconductor ◽  
Systematic Analysis

Geometric structure and electronic structure of wurtzite ZnO have been calculated adopting first principle plane wave ultrosoft pseudo potential method based on density functional theory, and band structure, electronic state density, differential charge distribution of ZnO have been subjected to systematic analysis, the results of which show that ZnO is a type of wide gap and direct gap semiconductor, with conduction band bottom and valence band top at the point Γ of Brillouin zone and valence band top showing obvious triply degenerateΓ7、Γ9、Γ7,while conduction band bottom beingΓ7. electronic structure calculation shows that Zn 3d narrow orbit between-6 and-4 eV has been fully filled with electrons and that O 2p wide orbit between-4 and 0 eV has also been fully filled with electron. In addition, charge density calculation shows that ZnO is metal oxide semiconductor with hybrid bond characterized by high ionicity and low covalent bond, accordingly, the above mentioned findings are superior to value of calculation mentioned in some documents.

Spatially Resolved Photoelectron Spectroscopy: Recent Progress and Future Plans

1990 ◽  
Vol 48 (2) ◽  
pp. 388-389
Author(s):  
A. M. Bradshaw
Keyword(s):  
Photoelectron Spectroscopy ◽  
Chemical Reactivity ◽  
Target Material ◽  
Orbital Energy ◽  
Light Sources ◽  
Analytical Technique ◽  
Hartree Fock ◽  
Spatially Resolved ◽  
Koopmans Theorem ◽  
Surface Analytical Technique

X-ray photoelectron spectroscopy (XPS or ESCA) was not developed by Siegbahn and co-workers as a surface analytical technique, but rather as a general probe of electronic structure and chemical reactivity. The method is based on the phenomenon of photoionisation: The absorption of monochromatic radiation in the target material (free atoms, molecules, solids or liquids) causes electrons to be injected into the vacuum continuum. Pseudo-monochromatic laboratory light sources (e.g. AlKα) have mostly been used hitherto for this excitation; in recent years synchrotron radiation has become increasingly important. A kinetic energy analysis of the so-called photoelectrons gives rise to a spectrum which consists of a series of lines corresponding to each discrete core and valence level of the system. The measured binding energy, EB, given by EB = hv−EK, where EK is the kineticenergy relative to the vacuum level, may be equated with the orbital energy derived from a Hartree-Fock SCF calculation of the system under consideration (Koopmans theorem).

Aldehyde gold clusters for molecular labeling

1995 ◽  
Vol 53 ◽  
pp. 858-859
Author(s):  
James F. Hainfeld ◽  
Frederic R. Furuya
Keyword(s):  
Covalent Bond ◽  
Aldehyde Group ◽  
Gold Clusters ◽  
Side Reactions ◽  
Amino Groups ◽  
Sodium Cyanoborohydride ◽  
Schiff’S Base ◽  
Protein Molecules ◽  
Hydroxysuccinimide Esters ◽  
Primary Amino

Glutaraldehyde is a useful tissue and molecular fixing reagents. The aldehyde moiety reacts mainly with primary amino groups to form a Schiff's base, which is reversible but reasonably stable at pH 7; a stable covalent bond may be formed by reduction with, e.g., sodium cyanoborohydride (Fig. 1). The bifunctional glutaraldehyde, (CHO-(CH2)3-CHO), successfully stabilizes protein molecules due to generally plentiful amines on their surface; bovine serum albumin has 60; 59 lysines + 1 α-amino. With some enzymes, catalytic activity after fixing is preserved; with respect to antigens, glutaraldehyde treatment can compromise their recognition by antibodies in some cases. Complicating the chemistry somewhat are the reported side reactions, where glutaraldehyde reacts with other amino acid side chains, cysteine, histidine, and tyrosine. It has also been reported that glutaraldehyde can polymerize in aqueous solution. Newer crosslinkers have been found that are more specific for the amino group, such as the N-hydroxysuccinimide esters, and are commonly preferred for forming conjugates. However, most of these linkers hydrolyze in solution, so that the activity is lost over several hours, whereas the aldehyde group is stable in solution, and may have an advantage of overall efficiency.

Structure of stacking faults in pyrite using TEM techniques

1992 ◽  
Vol 50 (1) ◽  
pp. 358-359
Author(s):  
Raja Subramanian ◽  
Kenneth S. Vecchio
Keyword(s):  
Lattice Structure ◽  
Stacking Faults ◽  
Covalent Bond ◽  
Group Symmetry ◽  
Iron Pyrite ◽  
Dislocation Glide ◽  
Partial Dislocations ◽  
Transmission Electron ◽  
Contrast Analysis ◽  
Chlorine Ions

The structure of stacking faults and partial dislocations in iron pyrite (FeS2) have been studied using transmission electron microscopy. Pyrite has the NaCl structure in which the sodium ions are replaced by iron and chlorine ions by covalently-bonded pairs of sulfur ions. These sulfur pairs are oriented along the <111> direction. This covalent bond between sulfur atoms is the strongest bond in pyrite with Pa3 space group symmetry. These sulfur pairs are believed to move as a whole during dislocation glide. The lattice structure across these stacking faults is of interest as the presence of these stacking faults has been preliminarily linked to a higher sulfur reactivity in pyrite. Conventional TEM contrast analysis and high resolution lattice imaging of the faulted area in the TEM specimen has been carried out.

Effect of Integral Proteins on Frozen Membrane Fracture

1980 ◽  
Vol 38 ◽  
pp. 756-759 ◽  
Author(s):  
S. Kirchanski ◽  
D. Branton
Keyword(s):  
Lipid Bilayers ◽  
Freeze Fracture ◽  
Covalent Bond ◽  
Erythrocyte Membranes ◽  
Glycophorin A ◽  
Experimental Protocol ◽  
Transmembrane Glycoprotein ◽  
Bond Breakage ◽  
Human Erythrocyte Membranes ◽  
Integral Proteins

We have investigated the effect of integral membrane proteins upon the fracturing of frozen lipid bilayers. This investigation has been part of an effort to develop freeze fracture labeling techniques and to assess the possible breakage of covalent protein bonds during the freeze fracture process. We have developed an experimental protocol utilizing lectin affinity columns which should detect small amounts of covalent bond breakage during the fracture of liposomes containing purified (1) glycophorin (a transmembrane glycoprotein of human erythrocyte membranes). To fracture liposomes in bulk, frozen liposomes are ground repeatedly under liquid nitrogen. Failure to detect any significant covalent bond breakage (contrary to (2)) led us to question the effectiveness of our grinding procedure in fracturing and splitting lipid bilayers.

STATIONARY AFTERGLOW STUDY OF THE SINGLY CHARGED ATOMIC IONS IN PURE AR AND KR

1979 ◽  
Vol 40 (C7) ◽  
pp. C7-51-C7-52
Author(s):  
M. Grössl ◽  
H. Helm ◽  
M. Langenwalter ◽  
T.D. Märk
Keyword(s):  
Atomic Ions ◽  
Singly Charged

Economic effects of monetary policy in Russia: What do large datasets tell us?

2020 ◽  
pp. 31-53 ◽  
Author(s):  
Anna A. Pestova ◽  
Natalia A. Rostova
Keyword(s):  
Monetary Policy ◽  
Interest Rate ◽  
Interest Rates ◽  
Economic Activity ◽  
Global Financial Crisis ◽  
Exchange Rate Regime ◽  
Aggregate Demand ◽  
Economic Effects ◽  
Theoretical Concepts ◽  
Empirical Estimates

Is the Bank of Russia able to control inflation and, at the same time, manage aggregate demand using its interest rate instruments? In other words, are empirical estimates of the effects of monetary policy in Russia consistent with the theoretical concepts and experience of advanced economies? This paper is aimed at addressing these issues. Unlike previous research, we employ “big data” — a large dataset of macroeconomic and financial data — to estimate the effects of monetary policy in Russia. We focus exclusively on the period after the 2008—2009 global financial crisis when the Bank of Russia announced the abandoning of its fixed ruble exchange rate regime and started to gradually transit to an interest rate management. Our estimation results do not confirm standard responses of key economic activity and price variables to tightening of monetary policy. Specifically, our estimates do not reveal a statistically significant restraining effect of the Bank of Russia’s policy of high interest rates on inflation in recent years. At the same time, we find a significant deteriorating effect of the monetary tightening on economic activity indicators: according to our conservative estimates, each of the key rate increases occurred in March and December 2014 had led to a decrease in the industrial production index by about 0.2 percentage points within a year.

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