scholarly journals Charge density studies of multicentre two-electron bonding of an anion radical at non-ambient temperature and pressure

IUCrJ ◽  
2021 ◽  
Vol 8 (4) ◽  
Author(s):  
Valentina Milašinović ◽  
Krešimir Molčanov ◽  
Anna Krawczuk ◽  
Nikita E. Bogdanov ◽  
Boris A. Zakharov ◽  
...  
Keyword(s):  
Charge Density ◽  
Radical Anion ◽  
Anion Radical ◽  
Ambient Pressure ◽  
Covalent Character ◽  
Charge Densities ◽  
Semiquinone Radicals ◽  
Temperature And Pressure ◽  
Covalent Interactions ◽  
Resolution Data

The variation of charge density of two-electron multicentre bonding (pancake bonding) between semiquinone radicals with pressure and temperature was studied on a salt of 5,6-dichloro-2,3-dicyanosemiquinone radical anion (DDQ) with 4-cyano-N-methylpyridinium cation (4-CN) using the Transferable Aspheric Atom Model (TAAM) refinement. The pancake-bonded radical dimers are stacked by non-bonding π-interactions. With rising pressure, the covalent character of interactions between radicals increases, and above 2.55 GPa, the electron density indicates multicentric covalent interactions throughout the stack. The experimental charge densities were verified and corroborated by periodic DFT computations. The TAAM approach has been tested and validated for atomic resolution data measured at ambient pressure; this work shows this approach can also be applied to diffraction data obtained at pressures up to several gigapascals.

Charge density of (−)-strychnine from 100 to 15 K, a comparison of four data sets

2005 ◽  
Vol 61 (1) ◽  
pp. 115-121 ◽  
Author(s):  
Marc Messerschmidt ◽  
Stephan Scheins ◽  
Peter Luger
Keyword(s):  
High Resolution ◽  
Charge Density ◽  
Data Sets ◽  
High Resolution Data ◽  
Charge Densities ◽  
Topological Parameters ◽  
Excellent Quality ◽  
Density Study ◽  
Resolution Data ◽  
Better Than

Strychnine has an interesting oligocyclic structure of seven condensed rings. It is easy to crystallize and gives crystals of excellent quality which diffract nicely to high regions in reciprocal space. It was thus chosen for a comparative charge-density study based on four high-resolution data sets (sin θ/λ ≥ 1.15 Å−1) that were measured with different experimental setups in the temperature range 100–15 K. In addition, a theoretical charge density was derived from a B3LYP/6-311++G(3df,3pd) calculation. The agreement expressed in bond topological parameters among the four experimental charge densities is better than between experiment and theory.

A Fluorine 1,2-Migration via Aryl Cation/Radical/Radical Anion/Radical Sequence

2013 ◽  
Vol 15 (15) ◽  
pp. 3926-3929 ◽  
Author(s):  
Luca Pretali ◽  
Daniele Dondi ◽  
Mila D’Angelantonio ◽  
Ilse Manet ◽  
Elisa Fasani ◽  
...  
Keyword(s):  
Radical Anion ◽  
Anion Radical ◽  
Cation Radical

Photoluminescence spectrum of tetracyanoquinodimethane crystals at 25 K: temperature and pressure dependence

1986 ◽  
Vol 64 (3) ◽  
pp. 277-281
Author(s):  
S. Desgreniers ◽  
L. Roubi ◽  
C. Carlone ◽  
H. D. Hochheimer
Keyword(s):  
Photoluminescence Spectrum ◽  
Anion Radical ◽  
Temperature Shift ◽  
Phonon Interaction ◽  
Electron Phonon Interaction ◽  
Stretching Vibration ◽  
Total Temperature ◽  
Temperature And Pressure ◽  
Low Pressures ◽  
Interaction Contribution

Using 488.0 and 514.5 nm laser radiation, we have obtained the luminescence spectrum of excited tetracyanoquinodimethane (TCNQ) crystals from 10 to 36 K at a pressure of 0 GPa. At 10 K, the luminescent peaks occur at 14 100, 15 000, 15 700 (±100), 16 300, 16 600, 16 800, and 17 200 (±50) cm−1. The temperature shift of the spectrum is −16 ± 7 cm−1∙K−1. At a constant temperature of 25 K, we followed the luminescent peaks as a function of pressure up to 8.5 GPa. The pressure shift of the luminescence, at low pressures, is −100 ± 50 cm−1∙GPa−1. We estimate that the volume-dilation contribution to the total temperature dependence is at most +2 cm−1∙K−1, in which case the electron–phonon-interaction contribution is −18 cm−1∙K−1. We have also examined the Raman spectrum at 25 K and have found the 1389 cm−1 ν4 (C=C) wing-stretching vibration of TCNQ−; its pressure behaviour is similar to that observed in TCNQ salts. The measurements were made on crystals grown very differently in two separate laboratories, and the effects induced by temperature or pressure were reversible. We attribute the luminescence to the 2B2g → 2B1μ transition of the TCNQ− anion radical, whose presence is due to impurities having a concentration of less than 0.01%.

Charge density studies on methylene blue – a potential anti-Alzheimer agent

2018 ◽  
Vol 73 (2) ◽  
pp. 99-108 ◽  
Author(s):  
Peter Luger ◽  
Birger Dittrich ◽  
Leonard Benecke ◽  
Hannes Sterzel
Keyword(s):  
Methylene Blue ◽  
Charge Density ◽  
Molecular Electrostatic Potential ◽  
Positive Charge ◽  
Atomic Charges ◽  
Charge Densities ◽  
Density Distributions ◽  
Atomic Properties ◽  
Counter Ions ◽  
Medical Interest

AbstractMotivated by the medical interest in methylene blue as potential anti-Alzheimer agent, the charge densities of three salt structures containing the methylene blue cation with nitrate (as dihydrate), chloride (as pentahydrate) and thiocyanate counter-ions were generated by application of the invariom formalism and examined. The so-obtained charge density distributions were analyzed using the QTAIM formalism to yield bond topological and atomic properties. The atomic charges on the methylene blue cation indicate a delocalized charge distribution; only a small positive charge on the sulfur atom was found. Electrostatic potentials mapped onto iso-surfaces of electron density for the cations, and for the methylene blue cations with anions, were compared. The effect of hydrogen disorder on the molecular electrostatic potential was investigated for the thiocyanate structure.

ELECTRICAL NONLINEAR PHENOMENA IN ROCKS

Geophysics ◽  
1973 ◽  
Vol 38 (1) ◽  
pp. 106-124 ◽  
Author(s):  
T. J. Katsube ◽  
R. H. Ahrens ◽  
L. S. Collett
Keyword(s):  
Critical Current Density ◽  
Charge Density ◽  
Critical Current ◽  
Current Density ◽  
Nonlinear Phenomena ◽  
Critical Charge ◽  
Charge Densities ◽  
Dry Electrode ◽  
Electrode Contact ◽  
Geophysical Technique

Evidence is presented in this paper on the electrical nonlinear phenomena occurring above a certain charge density at the electrode plates (critical charge density, [Formula: see text]) for a serpentinite sample with dry electrode contact and a galena sample using moist electrode contact. The critical charge density for the serpentinite sample is [Formula: see text] [Formula: see text]. In terms of critical current density, it is [Formula: see text] at [Formula: see text] hz, or [Formula: see text] at 10 hz. The galena sample shows two critical charge densities, where one is [Formula: see text] and the other is [Formula: see text]. In terms of critical current density, it is [Formula: see text] at [Formula: see text] hz, or [Formula: see text] at 10 hz for the first critical charge. The concept of “critical charge and nonlinearity” is similar to that of “decomposition voltage” of electrodes immersed in an electrolyte. The decomposition voltage is a characteristic of conductors immersed in liquids, and it varies according to the type of conductor. It is thus possible that the nonlinear study of minerals could form a basis of a new geophysical technique, especially in borehole logging, for detecting not only the existence, but also the type, of minerals in the ground.

ChemInform Abstract: Electron Transfer Photochemistry of Aromatic Imides and Phenylcyclopropane. Radical Anion-Radical Cation Cycloaddition.

ChemInform ◽  
1987 ◽  
Vol 18 (11) ◽  
Author(s):  
P. H. MAZZOCCHI ◽  
C. SOMICH ◽  
M. EDWARDS ◽  
T. MORGAN ◽  
H. L. AMMON
Keyword(s):  
Electron Transfer ◽  
Radical Cation ◽  
Radical Anion ◽  
Anion Radical

scholarly journals A Stable Binary BeB2 phase

2014 ◽  
Vol 4 (1) ◽  
Author(s):  
Changzeng Fan ◽  
Ye Jin ◽  
Jian Li ◽  
Xu Dong
Keyword(s):  
Phonon Dispersion ◽  
Population Analysis ◽  
Ambient Pressure ◽  
Mulliken Population ◽  
Dispersion Phase ◽  
Charge Density Difference ◽  
Total Interaction ◽  
Evolutionary Simulations ◽  
Covalent Interactions ◽  
New Phase

Abstract Potential crystal structures of BeB2 were explored using ab initio evolutionary simulations. A new phase with a Cmcm space group was uncovered. It was determined that the Cmcm phase is mechanically and dynamically stable and has a lower enthalpy, from ambient pressure up to 13 GPa, than any previously proposed phases, as measured using first-principles calculations. The crystal structure, phonon dispersion, phase transitions and mechanical and electronic properties of this phase were investigated. It was determined that the Cmcm phase may transform into the "Equation missing" phase at pressures higher than 13 GPa. The band structures and density of states reveal that the Cmcm phase is metallic. In addition, the Vickers hardness was calculated using three empirical models. To explain the origin of the hardness, charge density difference maps and a Mulliken population analysis were carried out, which demonstrated that there are strong covalent interactions between B atoms. By analyzing the Crystal Orbital Hamilton Population (COHP) diagrams, it was determined that the total interaction of the Be-B bonds is stronger than that of the B-B bonds, indicating a very complex bonding feature in the new phase. It was predicted that the new Cmcm phase is nearly absent of superconductivity.

Heat Flow Transducer Responses to Hyperbaric Environments

1980 ◽  
Vol 102 (3) ◽  
pp. 247-252 ◽  
Author(s):  
M. L. Nuckols
Keyword(s):  
Heat Flow ◽  
Ambient Pressure ◽  
Heat Fluxes ◽  
Constant Heat ◽  
Flow Transducer ◽  
Ambient Temperatures ◽  
Temperature And Pressure ◽  
Environmental Temperatures ◽  
Body Heat ◽  
Hyperbaric Conditions

The responses of heat flow transducers, used in the evaluation of convective body heat losses, have been investigated at hyperbaric environments. Environmental temperatures, pressures, and gas composition were varied while transducer responses to constant heat fluxes were observed. Ambient temperatures were varied between 3° and 40° C. Ambient pressures were varied between simulated depths of 0 and 1000 feet of seawater (445 psi). Transducer responses to heat fluxes varying between 0 and 250 watts/m2 are reported in the above temperature and pressure ranges within atmospheres of helium, nitrogen, and air. Ambient pressure variations were found to have little effect on the response of the heat flow transudcers to a constant heat source once appropriate temperature corrections were made. However, transducer response variations of up to 14 percent were observed when environmental gas compositions were varied at hyperbaric conditions.

Cohesive properties of metals as determined from atomic charge densities

1996 ◽  
Vol 74 (6) ◽  
pp. 870-874 ◽  
Author(s):  
Yoram Tal
Keyword(s):  
Charge Density ◽  
Ab Initio ◽  
Cohesive Energy ◽  
Atomic Charge ◽  
Metallic Elements ◽  
Transition Elements ◽  
Charge Densities ◽  
Cohesive Properties ◽  
Metallic Charge ◽  
Cohesive Energies

A direct relation between the charge density of a free atom, ρa(r), and the cohesive energy of the corresponding metal is proposed. This relation is based on an approximation for the metallic charge density, ρm(r), that is constructed from ρa(r) through [Formula: see text] being the atomic volume of the metallic atom, and R0 the corresponding Wigner–Seitz radius. The cohesive energy Ecoh is then related to [Formula: see text] through [Formula: see text] A systematic study of 29 metallic elements including the 3d and 4d transition elements shows that the proposed relation is, in general, at least as accurate as recent ab initio results. In the same fashion, an expression for the metallic bulk modulus is derived. This expression requires, in addition to [Formula: see text], the values of ρa(R0) and its first derivative ρ′a(R0). The computed bulk moduli are, again, at least as good as the ab initio ones for the set of metallic elements studied. Key words: cohesive energies, bulk moduli, charge density, transition elements.

scholarly journals Kaolin polytypes revisited ab initio

2008 ◽  
Vol 64 (2) ◽  
pp. 131-143 ◽  
Author(s):  
Patrick H. J. Mercier ◽  
Yvon Le Page
Keyword(s):  
Free Energy ◽  
Recent Literature ◽  
Ambient Pressure ◽  
Zero Temperature ◽  
Repeated Application ◽  
Energy Contribution ◽  
Energy Models ◽  
Unknown Reason ◽  
Temperature And Pressure ◽  
Experimental Structure

The well known 36 distinguishable transformations between adjacent kaolin layers are split into 20 energetically distinguishable transformations (EDT) and 16 enantiomorphic transformations, hereafter denoted EDT*. For infinitesimal energy contribution of interactions between non-adjacent layers, the lowest-energy models must result from either (a) repeated application of an EDT or (b) alternate application of an EDT and its EDT*. All modeling, quantum input preparation and interpretation was performed with Materials Toolkit, and quantum optimizations with VASP. Kaolinite and dickite are the lowest-energy models at zero temperature and pressure, whereas nacrite and HP-dickite are the lowest-enthalpy models under moderate pressures based on a rough enthalpy/pressure graph built from numbers given in the supplementary tables. Minor temperature dependence of this calculated 0 K graph would explain the bulk of the current observations regarding synthesis, diagenesis and transformation of kaolin minerals. Other stackings that we list have energies so competitive that they might crystallize at ambient pressure. A homometric pair of energetically distinguishable ideal models, one of them for nacrite, is exposed. The printed experimental structure of nacrite correctly corresponds to the stable member of the pair. In our opinion, all recent literature measurements of the free energy of bulk kaolinite are too negative by ∼ 15 kJ mol−1 for some unknown reason.

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