Benzenoid hydrocarbon aromaticity in terms of charge density descriptors

1997 ◽  
Vol 75 (9) ◽  
pp. 1174-1181 ◽  
Author(s):  
S.T. Howard ◽  
T.M. Krygowski
Keyword(s):  
Charge Density ◽  
Critical Point ◽  
Critical Points ◽  
Electron Distribution ◽  
Stationary Points ◽  
Bond Critical Point ◽  
Total Density ◽  
Benzenoid Hydrocarbon ◽  
Hartree Fock ◽  
Point Data

Hartree–Fock/6-31G** calculations on the benzenoid hydrocarbons benzene, naphthalene, phenanthrene, anthracene, pyrene, tetracene, triphenylene, chrysene, perylene, and coronene are used to investigate the link between aromaticity and the electron distribution. Topological charge density analysis is used, concentrating on the electron distribution ρ (and its Hessian) at bond and ring critical points. With regard to the bond critical point data, it is shown that ρc, [Formula: see text]ρc, and the bond "ellipticity" ε are closely correlated with the bond lengths so, as aromaticity indicators, they have little to add over and above existing indices based on structure. However, the same properties evaluated at the ring critical points in the total density, and also at the equivalent stationary points in the π and σ densities, correlate closely with two different aromaticity indices (one based on structure, the other on magnetic properties), the curvature of ρ perpendicular to the ring plane giving (marginally) the best results. Hence a ring critical point (RCP) index is proposed as a way of quantifying aromaticity, based directly on the electron distribution. Keywords: quantum chemistry, electron density, aromaticity, aromaticity index, HOMA, NICS.

scholarly journals A method to estimate statistical errors of properties derived from charge-density modelling

2018 ◽  
Vol 74 (3) ◽  
pp. 170-183 ◽  
Author(s):  
Bertrand Fournier ◽  
Benoît Guillot ◽  
Claude Lecomte ◽  
Eduardo C. Escudero-Adán ◽  
Christian Jelsch
Keyword(s):  
Charge Density ◽  
Least Squares ◽  
Critical Point ◽  
Critical Points ◽  
Property Values ◽  
Density Model ◽  
Interaction Energies ◽  
Topological Properties ◽  
A Charge ◽  
Density Modelling

Estimating uncertainties of property values derived from a charge-density model is not straightforward. A methodology, based on calculation of sample standard deviations (SSD) of properties using randomly deviating charge-density models, is proposed with theMoProsoftware. The parameter shifts applied in the deviating models are generated in order to respect the variance–covariance matrix issued from the least-squares refinement. This `SSD methodology' procedure can be applied to estimate uncertainties ofanyproperty related to a charge-density model obtained by least-squares fitting. This includes topological properties such as critical point coordinates, electron density, Laplacian and ellipticity at critical points and charges integrated over atomic basins. Errors on electrostatic potentials and interaction energies are also available now through this procedure. The method is exemplified with the charge density of compound (E)-5-phenylpent-1-enylboronic acid, refined at 0.45 Å resolution. The procedure is implemented in the freely availableMoProprogram dedicated to charge-density refinement and modelling.

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).

Intramolecular mode coupling of the isotopomers of water: a non-scalar charge density-derived perspective

2020 ◽  
Vol 22 (4) ◽  
pp. 2509-2520
Author(s):  
Tian Tian ◽  
Tianlv Xu ◽  
Steven R. Kirk ◽  
Ian Tay Rongde ◽  
Yong Boon Tan ◽  
...  
Keyword(s):  
Charge Density ◽  
Critical Point ◽  
Mode Coupling ◽  
Bond Critical Point ◽  
Scalar Charge

Left: The BCP trajectories T(s) for H2O for the bending (Q1) mode, the axes labels of the trajectory T(s). The green spheres correspond to the bond critical point (BCPs). Right: The corresponding T(s) for H2O for the symmetric-stretch (Q2) mode.

Study of charge transfer in FeTi

1983 ◽  
Vol 41 ◽  
pp. 296-297
Author(s):  
J. Taft∅
Keyword(s):  
Charge Transfer ◽  
Charge Distribution ◽  
Electron Scattering ◽  
Periodic System ◽  
Electron Distribution ◽  
Scattering Amplitude ◽  
Transition Elements ◽  
Hartree Fock ◽  
Cscl Structure ◽  
The Right

It is well known that for reflections corresponding to large interplanar spacings (i.e., sin θ/λ small), the electron scattering amplitude, f, is sensitive to the ionicity and to the charge distribution around the atoms. We have used this in order to obtain information about the charge distribution in FeTi, which is a candidate for storage of hydrogen. Our goal is to study the changes in electron distribution in the presence of hydrogen, and also the ionicity of hydrogen in metals, but so far our study has been limited to pure FeTi. FeTi has the CsCl structure and thus Fe and Ti scatter with a phase difference of π into the 100-ref lections. Because Fe (Z = 26) is higher in the periodic system than Ti (Z = 22), an immediate “guess” would be that Fe has a larger scattering amplitude than Ti. However, relativistic Hartree-Fock calculations show that the opposite is the case for the 100-reflection. An explanation for this may be sought in the stronger localization of the d-electrons of the first row transition elements when moving to the right in the periodic table. The tabulated difference between fTi (100) and ffe (100) is small, however, and based on the values of the scattering amplitude for isolated atoms, the kinematical intensity of the 100-reflection is only 5.10-4 of the intensity of the 200-reflection.

scholarly journals Tuning the charge density wave quantum critical point and the appearance of superconductivity in TiSe2

2021 ◽  
Vol 3 (3) ◽  
Author(s):  
Sangyun Lee ◽  
Tae Beom Park ◽  
Jihyun Kim ◽  
Soon-Gil Jung ◽  
Won Kyung Seong ◽  
...  
Keyword(s):  
Charge Density ◽  
Critical Point ◽  
Charge Density Wave ◽  
Density Wave ◽  
Quantum Critical Point ◽  
Quantum Critical

scholarly journals Multiband nodeless superconductivity near the charge-density-wave quantum critical point in ZrTe 3− x Se x

2016 ◽  
Vol 25 (7) ◽  
pp. 077403
Author(s):  
Shan Cui ◽  
Lan-Po He ◽  
Xiao-Chen Hong ◽  
Xiang-De Zhu ◽  
Cedomir Petrovic ◽  
...  
Keyword(s):  
Charge Density ◽  
Critical Point ◽  
Charge Density Wave ◽  
Density Wave ◽  
Quantum Critical Point ◽  
Quantum Critical

Electronegativity and Bader's bond critical point

1992 ◽  
Vol 13 (7) ◽  
pp. 912-918 ◽  
Author(s):  
Sanchita Hati ◽  
Dipankar Datta
Keyword(s):  
Critical Point ◽  
Bond Critical Point

Phase space correspondence between Jordan and Einstein frames

2021 ◽  
pp. 2150087
Author(s):  
Amin Salehi
Keyword(s):  
Phase Space ◽  
Critical Point ◽  
Critical Points ◽  
Dynamical Behavior ◽  
Cosmological Parameters ◽  
Jordan Frame ◽  
Field Equations ◽  
Theories Of Gravity ◽  
The Stability ◽  
Jordan And Einstein Frames

Scalar–tensor theories of gravity can be formulated in the Einstein frame or in the Jordan frame (JF) which are related with each other by conformal transformations. Although the two frames describe the same physics and are equivalent, the stability of the field equations in the two frames is not the same. Here, we implement dynamical system and phase space approach as a robustness tool to investigate this issue. We concentrate on the Brans–Dicke theory in a Friedmann–Lemaitre–Robertson–Walker universe, but the results can easily be generalized. Our analysis shows that while there is a one-to-one correspondence between critical points in two frames and each critical point in one frame is mapped to its corresponds in another frame, however, stability of a critical point in one frame does not guarantee the stability in another frame. Hence, an unstable point in one frame may be mapped to a stable point in another frame. All trajectories between two critical points in phase space in one frame are different from their corresponding in other ones. This indicates that the dynamical behavior of variables and cosmological parameters is different in two frames. Hence, for those features of the study, which focus on observational measurements, we must use the JF where experimental data have their usual interpretation.

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