CTED: the new aromaticity index based on corrected total electron density at bond critical points

2014 ◽  
Vol 27 (5) ◽  
pp. 380-386 ◽  
Author(s):  
Ahmet Tokatlı ◽  
Fatih Ucun
Keyword(s):  
Electron Density ◽  
Critical Points ◽  
Total Electron Density ◽  
Total Electron ◽  
Aromaticity Index

Electrostatic properties of ammonium fluoride and deuterated ice-Ih

1996 ◽  
Vol 74 (6) ◽  
pp. 943-950 ◽  
Author(s):  
C.G. Van Beek ◽  
J. Overeem ◽  
J.R. Ruble ◽  
B.M. Craven
Keyword(s):  
Dipole Moment ◽  
Density Distribution ◽  
Electron Density ◽  
Critical Points ◽  
Electron Density Distribution ◽  
Ammonium Fluoride ◽  
Total Electron Density ◽  
Total Electron ◽  
Space Group ◽  
X Ray

New single crystal X-ray diffraction data have been collected at reduced temperature (120 K) and high resolution (sinθ/λ ≤ 1.34 Å−1) for ammonium fluoride and for heavy ice-Ih, (D2O) in order to determine the detailed electron density distribution in these structures. The crystals are isostructural. Ammonium fluoride, NH4F, is hexagonal with space group P63mc, a = 4.4365(3), c = 7.1672(5) Å, Z = 2. Ice-Ih, D2O, is hexagonal with space group P63/mmc, a = 4.4950(5), c = 7.3170(10) Å, Z = 4. The X-ray data were collected with Nb-filtered MoKα radiation (λ = 0.7093 Å). Refinements with Stewart's rigid pseudoatom model gave R(F2) = 0.016 for 292 reflections for NH4F and R(F2) = 0.023 for 296 reflections for ice-Ih. Hydrogen nuclear positions and mean-square displacements were taken from previous neutron diffraction studies. The structures each contain two crystallographically distinct H(D) atoms, namely, those with N-H or O-D directed along the c-axis and those that are directed tetrahedrally with respect to c. For NH4F, maps of the total electron density, the total electrostatic potential, and the values of the Laplacian at the bond critical points show that the bonding interactions involving both kinds of H atom are the same within experimental error. Similar results are obtained for ice-Ih although there are complications and limitations owing to the disorder in the structure. Nevertheless, the pseudoatom model enables the electron density distribution to be determined for an ordered water molecule isolated from the crystal structure. The estimated molecular dipole moment for water in ice-Ih, is 2.1 debye. Key words: electron density, bond critical points, hydrogen bonding, water dipole moment.

Revisiting the charge density analysis of 2,5-dichloro-1,4-benzoquinone at 20 K

2017 ◽  
Vol 73 (4) ◽  
pp. 654-659 ◽  
Author(s):  
Zhijie Chua ◽  
Bartosz Zarychta ◽  
Christopher G. Gianopoulos ◽  
Vladimir V. Zhurov ◽  
A. Alan Pinkerton
Keyword(s):  
Charge Density ◽  
Electron Density ◽  
Topological Analysis ◽  
Diffraction Measurement ◽  
X Ray Diffraction ◽  
Total Electron Density ◽  
Total Electron ◽  
Structure Factors ◽  
Density Analysis ◽  
Experimental Charge Density

A high-resolution X-ray diffraction measurement of 2,5-dichloro-1,4-benzoquinone (DCBQ) at 20 K was carried out. The experimental charge density was modeled using the Hansen–Coppens multipolar expansion and the topology of the electron density was analyzed in terms of the quantum theory of atoms in molecules (QTAIM). Two different multipole models, predominantly differentiated by the treatment of the chlorine atom, were obtained. The experimental results have been compared to theoretical results in the form of a multipolar refinement against theoretical structure factors and through direct topological analysis of the electron density obtained from the optimized periodic wavefunction. The similarity of the properties of the total electron density in all cases demonstrates the robustness of the Hansen–Coppens formalism. All intra- and intermolecular interactions have been characterized.

Electron densities and the VSEPR model of molecular geometry

1992 ◽  
Vol 70 (3) ◽  
pp. 742-750 ◽  
Author(s):  
R. J. Gillespie
Keyword(s):  
Electron Density ◽  
Present Status ◽  
Electron Pair ◽  
Molecular Geometry ◽  
Physical Basis ◽  
Valence Shell ◽  
Electron Densities ◽  
Total Electron Density ◽  
Total Electron

This paper reviews the present status of the VSEPR model of molecular geometry in relation to electron densities. The discussion is based on the electron pair domain version of this model. The fundamental postulates of the model are summarized and illustrated by a discussion of the structures of some molecules with five and seven electron pair domains in the valence shell, including the recently discovered ions XeF5− and XeOF6−. The total electron density does not provide any obvious support for the model and although electron density deformation maps do provide some support they are not always reliable. The Laplacian of the electron density, however, shows the presence of valence shell charge concentrations that correspond closely in number and properties to the electron pair domains of the VSEPR model. This correspondence between electron pair domains and valence shell charge concentrations provides a physical basis for a better understanding of the VSEPR model. Keywords: VSEPR model, electron densities, molecular geometry, Laplacian of the electron density, electron pair domain.

Total electron density from thes-electron density

1998 ◽  
Vol 57 (5) ◽  
pp. 3458-3461 ◽  
Author(s):  
Á. Nagy ◽  
E. Bene
Keyword(s):  
Electron Density ◽  
Total Electron Density ◽  
Total Electron

scholarly journals Early results from the Whisper instrument on Cluster: an overview

2001 ◽  
Vol 19 (10/12) ◽  
pp. 1241-1258 ◽  
Author(s):  
P. M. E. Décréau ◽  
P. Fergeau ◽  
V. Krasnoselskikh ◽  
E. Le Guirriec ◽  
M. Lévêque ◽  
...  
Keyword(s):  
Electron Density ◽  
Small Scale ◽  
Data Sets ◽  
Total Density ◽  
Total Electron Density ◽  
Data Set ◽  
Total Electron ◽  
Density Data ◽  
Early Results ◽  
Natural Emissions

Abstract. The Whisper instrument yields two data sets: (i) the electron density determined via the relaxation sounder, and (ii) the spectrum of natural plasma emissions in the frequency band 2–80 kHz. Both data sets allow for the three-dimensional exploration of the magnetosphere by the Cluster mission. The total electron density can be derived unambiguously by the sounder in most magnetospheric regions, provided it is in the range of 0.25 to 80 cm-3 . The natural emissions already observed by earlier spacecraft are fairly well measured by the Whisper instrument, thanks to the digital technology which largely overcomes the limited telemetry allocation. The natural emissions are usually related to the plasma frequency, as identified by the sounder, and the combination of an active sounding operation and a passive survey operation provides a time resolution for the total density determination of 2.2 s in normal telemetry mode and 0.3 s in burst mode telemetry, respectively. Recorded on board the four spacecraft, the Whisper density data set forms a reference for other techniques measuring the electron population. We give examples of Whisper density data used to derive the vector gradient, and estimate the drift velocity of density structures. Wave observations are also of crucial interest for studying small-scale structures, as demonstrated in an example in the fore-shock region. Early results from the Whisper instrument are very encouraging, and demonstrate that the four-point Cluster measurements indeed bring a unique and completely novel view of the regions explored.Key words. Space plasma physics (instruments and techniques; discontinuities, general or miscellaneous)

Acrylonitrile (AN)–Cu9(100) interfaces: Electron distribution and nature of bonded interactions

2003 ◽  
Vol 81 (6) ◽  
pp. 542-554 ◽  
Author(s):  
Petar M Mitrasinovic
Keyword(s):  
Electron Density ◽  
Molecular Orbital ◽  
Density Functional ◽  
Electron Distribution ◽  
Atomic Orbital ◽  
Interfacial Interactions ◽  
Total Electron Density ◽  
Total Electron ◽  
Topological Features ◽  
The One

There is a fundamental interest in the investigation of the interfacial interactions and charge migration processes between organic molecules and metallic surfaces from a theoretical standpoint. Quantum mechanical (QM) concepts of bonding are contrasted, and the vital importance of using combined QM methods to explore the nature of the interfacial interactions is established. At the one-electron level, the charge distribution and nature of bonded interactions at the AN–Cu9(100) (neutral and charged (–1)) interfaces are investigated by both the Becke (B) – Vosko (V) – Wilk (W) – Nusair (N)/DZVP density functional theory (DFT) method and the MP2/6–31+G* strategy within the conceptual framework provided by natural bond orbital (NBO) – natural atomic orbital (NAO) population analysis and Atoms-In-Molecules (AIM) theory. By this approach, the interfacial interactions are given physical definitions free of any assumptions and are visualized by using the topological features of the total electron density. A natural link between the electron density on the one side and the shapes (not energies) of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) on the other side is clarified. The question of whether the spatial extents of the HOMO and LUMO resemble the corresponding spatial maps of the negative (charge locally concentrated) and positive (charge locally depleted) Laplacian of the total electron density in [AN–Cu9(100)]–1 is addressed.Key words: AN–Cu9(100) interfaces, NBO–NAO population, electron distribution, AIM, bonded interactions.

First Principles Investigations on the Supramolecular Structure of 1,5-Diaminotetrazole

2012 ◽  
Vol 554-556 ◽  
pp. 65-69
Author(s):  
He Lin ◽  
Shun Guan Zhu ◽  
Lin Zhang ◽  
Xin Hua Peng ◽  
Hong Zhen Li
Keyword(s):  
Hydrogen Bonds ◽  
Electron Density ◽  
First Principles ◽  
Supramolecular Structure ◽  
First Principles Calculations ◽  
Generalized Gradient ◽  
Intermolecular Hydrogen Bonds ◽  
Total Electron Density ◽  
Population Total ◽  
Total Electron

The supramolecular structure of 1,5-diaminotetrazole was investigated by first principles calculations, based on the plane-wave psedopotential method. The exchange-correlations potential was performed with the Perdew-Burke-Ernzerhof (PBE) functional of generalized gradient approximation (GGA). The Muliken population, total electron density and electron density difference were calculated. As a result, there are strong intramolecular and intermolecular hydrogen bonds among 1,5-diaminotetrazole molecules. The mainly reason for the formation of supramolecular structure of 1,5-diaminotetrazole is that the intermolecular hydrogen bonds of N(5)－H(5B)…N(4) and N(6)－H(6)…N(2).Moreover, chemical bond analysis showed that there are strong non-bond actions and the N(1)－N(5) bond seriously distorted was observed. The performance of 1,5-diaminotetrazole is quite related with the supramolecular structure.

Intermolecular interactions, charge-density distribution and the electrostatic properties of pyrazinamide anti-TB drug molecule: an experimental and theoretical charge-density study

2014 ◽  
Vol 70 (3) ◽  
pp. 568-579 ◽  
Author(s):  
Gnanasekaran Rajalakshmi ◽  
Venkatesha R. Hathwar ◽  
Poomani Kumaradhas
Keyword(s):  
Charge Density ◽  
Electron Density ◽  
Intermolecular Interactions ◽  
Electrostatic Potential ◽  
Density Functional ◽  
Direct Methods ◽  
Hirshfeld Surface ◽  
Basis Set ◽  
Total Electron Density ◽  
Total Electron

An experimental charge-density analysis of pyrazinamide (a first line antitubercular drug) was performed using high-resolution X-ray diffraction data [(sin θ/λ)max= 1.1 Å−1] measured at 100 (2) K. The structure was solved by direct methods usingSHELXS97 and refined bySHELXL97. The total electron density of the pyrazinamide molecule was modeled using the Hansen–Coppens multipole formalism implemented in theXDsoftware. The topological properties of electron density determined from the experiment were compared with the theoretical results obtained fromCRYSTAL09at the B3LYP/6-31G** level of theory. The crystal structure was stabilized by N—H...N and N—H...O hydrogen bonds, in which the N3—H3B...N1 and N3—H3A...O1 interactions form two types of dimers in the crystal. Hirshfeld surface analysis was carried out to analyze the intermolecular interactions. The fingerprint plot reveals that the N...H and O...H hydrogen-bonding interactions contribute 26.1 and 18.4%, respectively, of the total Hirshfeld surface. The lattice energy of the molecule was calculated using density functional theory (B3LYP) methods with the 6-31G** basis set. The molecular electrostatic potential of the pyrazinamide molecule exhibits extended electronegative regions around O1, N1 and N2. The existence of a negative electrostatic potential (ESP) region just above the upper and lower surfaces of the pyrazine ring confirm the π-electron cloud.

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