INDO calculations of spin densities. II. Further calculations on nickel(II) complexes and on a variety of acetylacetone complexes

1971 ◽  
Vol 24 (1) ◽  
pp. 31 ◽  
Author(s):  
MJ Scarlett ◽  
AT Casey ◽  
RA Craig
Keyword(s):  
Spin Density ◽  
Aliphatic Amines ◽  
Indo Method ◽  
Aromatic Nitriles ◽  
Indo Calculations ◽  
Spin Densities

Calculations of spin density on the ligand have been made by the INDO method on nickel(II) complexes of quinoline N-oxides, water, ammonia, aliphatic amines, aromatic nitriles, and isonitriles as well as on the acetylacetonates of a variety of metals. Three cases are distinguished: (1) the ligand could be considered purely as a cation or anion; (2) the ligand could be considered as a hybrid of cation and anion; (3) neither of these approaches is satisfactory, indicating that neglect of metal orbitals causes serious errors.

Effects of Temperature and Charge Depletion on the Spin Density in Hydrogenated Amorphous Silicon

1991 ◽  
Vol 219 ◽  
Author(s):  
J.-K. Lee ◽  
E. A. Schiff
Keyword(s):  
Spin Density ◽  
Negative Charge ◽  
Temperature Dependent ◽  
Defect Model ◽  
Depletion Width ◽  
Initial Charge ◽  
Effects Of Temperature ◽  
Hydrogenated Amorphous ◽  
Spin Densities ◽  
Charge Depletion

ABSTRACTThe dependence of the spin density upon temperature and charge depletion is calculated based on the standard defect model in a-Si:H of a D-center with positive, neutral, and negative charge states. The results are compared with recent measurements of depletion width modulated spin densities and temperature-dependent spin densities. It is shown that the initial charge density assumed for the defect system substantially affects conclusions regarding electronic correlation energies drawn from the measurements.

ESR Studies on 205Tl Hyperfine Couplings in the Radical Cations of Tl(III)Porphyrins

1974 ◽  
Vol 29 (12) ◽  
pp. 1827-1833 ◽  
Author(s):  
Chr. Mengersen ◽  
J. Subramanian ◽  
J.-H. Fuhrhop ◽  
K. M. Smith
Keyword(s):  
Spin Density ◽  
Spin Polarization ◽  
Radical Cations ◽  
Esr Spectra ◽  
Cation Radicals ◽  
Bilinear Relation ◽  
Tetraphenyl Porphyrin ◽  
Pi Orbitals ◽  
Spin Densities ◽  
Hyperfine Couplings

The isotropic 205Tl hyperfine couplings obtained from the ESR spectra of the radical cations of Tl (III) meso tetraphenyl porphyrin (TPP), octaethyl porphyrin (OEP) and octaethyl chlorin (OEC) are reported. The radical cations were generated by electrooxidation in dichloromethane as solvent. A Karplus-Fraenkel type bilinear relation is used to interpret the 205Tl couplings, taking into account the sigma-pi spin polarization of Tl -N bonds by the spin density at the nitrogen atoms in the ligand as well as the direct pi interaction of the orbitals of Tl with the pi orbitals of the ligand. It is shown that for the cation radicals of Tl porphyrins, both these mechanisms contribute to the Tl couplings whereas for the cation radicals of Co- and Zn-porphyrins the sigma-pi polarization alone is sufficient to account for the metal hyperfine couplings. It is suggested that Tl-hyperfine couplings can be used to estimate the nitrogen spin densities of porphyrin radical systems when the nitrogen splittings are not resolved in the ESR spectra.

MO Calculations of Some Thymine Radicals at the INDO Level

1976 ◽  
Vol 31 (7-8) ◽  
pp. 371-376 ◽  
Author(s):  
E Westhof ◽  
M Van Rooten
Keyword(s):  
Double Bond ◽  
Spin Density ◽  
Hydrogen Abstraction ◽  
Mo Calculations ◽  
Methyl Group ◽  
Hydrogen Addition ◽  
Indo Calculations

Abstract The results of MO INDO calculations of some thymine radicals are presented. These include as well as the hydrogen addition radicals the hydroxyl addition radicals to C5 and to C6 of the C5=C6 double bond of the thymine molecule. The radicals resulting from hydrogen abstraction from the methyl group and from the nitrogen N1 are also studied. Except for radicals where the main spin density is localized on nitrogen atoms, the agreement between experimental and theoretical couplings is satisfactory.

scholarly journals Einstein–Cartan–Dirac gravity with U(1) symmetry breaking

2019 ◽  
Vol 79 (12) ◽  
Author(s):  
Francisco Cabral ◽  
Francisco S. N. Lobo ◽  
Diego Rubiera-Garcia
Keyword(s):  
Spin Density ◽  
Affine Connection ◽  
New Physics ◽  
Energy Tensor ◽  
Field Equations ◽  
Antisymmetric Part ◽  
Stress Energy ◽  
Physical Effects ◽  
Cartan Theory ◽  
Spin Densities

AbstractEinstein–Cartan theory is an extension of the standard formulation of General Relativity where torsion (the antisymmetric part of the affine connection) is non-vanishing. Just as the space-time metric is sourced by the stress-energy tensor of the matter fields, torsion is sourced via the spin density tensor, whose physical effects become relevant at very high spin densities. In this work we introduce an extension of the Einstein–Cartan–Dirac theory with an electromagnetic (Maxwell) contribution minimally coupled to torsion. This contribution breaks the U(1) gauge symmetry, which is suggested by the possibility of a torsion-induced phase transition in the early Universe, yielding new physics in extreme (spin) density regimes. We obtain the generalized gravitational, electromagnetic and fermionic field equations for this theory, estimate the strength of the corrections, and discuss the corresponding phenomenology. In particular, we briefly address some astrophysical considerations regarding the relevance of the effects which might take place inside ultra-dense neutron stars with strong magnetic fields (magnetars).

scholarly journals Linear Response Functions of Densities and Spin Densities for Systematic Modeling of the QM/MM Approach for Mono- and Poly-Nuclear Transition Metal Systems

Molecules ◽  
2019 ◽  
Vol 24 (4) ◽  
pp. 821
Author(s):  
Colin Kitakawa ◽  
Tomohiro Maruyama ◽  
Jinta Oonari ◽  
Yuki Mitsuta ◽  
Takashi Kawakami ◽  
...  
Keyword(s):  
Quantum Mechanics ◽  
Transition Metal ◽  
Spin Density ◽  
Linear Response ◽  
Transition Metal Ions ◽  
Open Shell ◽  
Reaction Centers ◽  
Oxygen Evolving ◽  
The Relationship ◽  
Spin Densities

We applied our analysis, based on a linear response function of density and spin density, to two typical transition metal complex systems-the reaction centers of P450, and oxygen evolving center in Photosystem II, both of which contain open-shell transition metal ions. We discuss the relationship between LRF of electron density and spin density and the types of units and interactions of the systems. The computational results are discussed in relation to quantum mechanics (QM) cluster and quantum mechanics/molecular mechanics (QM/MM) modeling that are employed to compute the reaction centers of enzymes.

SPIN DENSITY OF SPIN-FREE VALENCE BOND WAVE FUNCTIONS AND ITS IMPLEMENTATION IN VB2000

2008 ◽  
Vol 07 (04) ◽  
pp. 853-867 ◽  
Author(s):  
JIABO LI ◽  
BRIAN J. DUKE ◽  
THOMAS M. KLAPÖTKE ◽  
ROY MCWEENY
Keyword(s):  
Spin Density ◽  
Valence Bond ◽  
Wave Functions ◽  
Free Valence ◽  
Group Function ◽  
Allyl Radical ◽  
The 1960S ◽  
Spin Density Calculation ◽  
New Formulation ◽  
Spin Densities

The expressions for computing the spin density of spin-free valence bond wave functions are derived based on the bonded tableaux approach. The new expressions, although similar to the original forms given by Cooper and McWeeny in the 1960s, are simpler and thus easier for coding. The new formulation was implemented in VB2000, an ab initio valence bond program based on algebrant algorithm and group function theory. The spin density calculation for multi-group VB wave functions is also briefly discussed. As examples of applications, the spin densities of allyl radical and diazide anion [Formula: see text] were computed at different VB levels.

scholarly journals The interplay between spin densities and magnetic superexchange interactions: case studies of mono- and trinuclear bis(oxamato)-type complexes

2017 ◽  
Vol 8 ◽  
pp. 2245-2256 ◽  
Author(s):  
Azar Aliabadi ◽  
Bernd Büchner ◽  
Vladislav Kataev ◽  
Tobias Rüffer
Keyword(s):  
Magnetic Properties ◽  
Transition Metal ◽  
Metal Complexes ◽  
Density Distribution ◽  
Case Studies ◽  
Spin Density ◽  
Transition Metal Complexes ◽  
Chemical Structures ◽  
Molecular Spin ◽  
Spin Densities

For future molecular spintronic applications the possibility to modify and tailor the magnetic properties of transition-metal complexes is very promising. One of such possibilities is given by the countless derivatization offered by carbon chemistry. They allow for altering chemical structures and, in doing so, to tune magnetic properties of molecular spin-carrying compounds. With emphasis on the interplay of the spin density distribution of mononuclear and magnetic superexchange couplings of trinuclear bis(oxamato)-type complexes we review on efforts on such magneto-structural correlations.

Time Dependence of the Metastable, Optically-Induced Esr in a-Si:H

1986 ◽  
Vol 70 ◽  
Author(s):  
C. Lee ◽  
W. D. Ohlsen ◽  
P. C. Taylor
Keyword(s):  
Time Dependence ◽  
Spin Density ◽  
Power Law ◽  
White Light ◽  
Monochromatic Light ◽  
Extended Range ◽  
Unique Power ◽  
Spin Densities ◽  
Optically Induced

ABSTRACTThe occurrence of optically-induced, metastable changes in the paramagnetism in films of a-Si:H is well known. The effect was first observed with white light in powdered samples, but recent experiments with both white and monochromatic light incident on films on substrates have observed a similar effect. This optically-induced ESR appears to be stable at temperatures < 400 K. Typical inducing curves for samples with initial dark spin densities ns > 1016 spins/cm3 approach a power law behavior (ns ∼ t1 / 3) at long times. However, when the dark spin density is less than 1016 spins/cm3, the samples exhibit an inducing curve (on a log-log scale) with a continuously decreasing slope. The curve does not exhibit a unique power law behavior over an extended range of time and is at all times < t1 / 3.

scholarly journals Insights on spin delocalization and spin polarization mechanisms in crystals of azido copper(II) dinuclear complexes through the electron spin density Source Function

2017 ◽  
Vol 73 (4) ◽  
pp. 565-583 ◽  
Author(s):  
Carlo Gatti ◽  
Giovanni Macetti ◽  
Leonardo Lo Presti
Keyword(s):  
Spin Density ◽  
Spin Polarization ◽  
Source Function ◽  
Reference Points ◽  
Dinuclear Complexes ◽  
Azido Group ◽  
Local Spin ◽  
Whole Space ◽  
Spin Delocalization ◽  
Spin Densities

The Source Function (SF) tool was applied to the analysis of thetheoreticalspin density in azido CuIIdinuclear complexes, where the azido group, acting as a coupler between the CuIIcations, is linked to the metal centres either in an end-on or in an end–end fashion. Results for only the former structural arrangement are reported in the present paper. The SF highlights to which extent the magnetic centres contribute to determine the local spin delocalization and polarization at any point in the dimetallic complex and whether an atom or group of atoms of the ligands act in favour or against a given local spin delocalization/polarization. Ball-and-stick atomic SF percentage representations allow for a visualization of the magnetic pathways and of the specific role played by each atom along these paths, at given reference points. Decomposition of SF contributions in terms of a magnetic and of a relaxation component provides further insight. Reconstruction of partial spin densities by means of the Source Function has for the first time been introduced. At variance with the standard SF percentage representations, such reconstructions offer a simultaneous view of the sources originating from specific subsets of contributing atoms, in a selected molecular plane or in the whole space, and are therefore particularly informative. The SF tool is also used to evaluate the accuracy of the analysed spin densities. It is found that those obtained at the unrestricted B3LYP DFT level, relative to those computed at the CASSCF(6,6) level, greatly overestimate spin delocalization to the ligands, but comparatively underestimate magnetic connection (spin transmission) among atoms, along the magnetic pathways. As a consequence of its excessive spin delocalization, the UB3LYP method also overestimates spin polarization mechanisms between the paramagnetic centres and the ligands. Spin delocalization measures derived from the refinement of Polarized Neutron Diffraction data seem in general superior to those obtained through the DFT UB3LYP approach and closer to the far more accurate CASSCF results. It is also shown that a visual agreement on the spin-resolved electron densities ραand ρβderived from different approaches does not warrant a corresponding agreement between their associated spin densities.

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