Structural isomers and tautomerism of chlorophyll a in the ground state studied by semiempirical MNDO-d method

2004 ◽  
Vol 681 (1-3) ◽  
pp. 213-224 ◽  
Author(s):  
M Nsangou ◽  
A Ben Fredj ◽  
N Jaı̈dane ◽  
M.G Kwato Njock ◽  
Z Ben Lakhdar
Keyword(s):  
Chlorophyll A ◽  
Ground State ◽  
Structural Isomers ◽  
Semiempirical Mndo

scholarly journals GGA/PBE study of the spin isomers of Fe34,40, Co23,34, and Co12Cu Clusters with Selected Geometries

2017 ◽  
Vol 56 (3) ◽  
Author(s):  
Faustino Aguilera-Granja ◽  
Andrés Vega ◽  
Luis Carlos Balbás
Keyword(s):  
Ground State ◽  
Density Functional ◽  
Energy Difference ◽  
Many Body ◽  
Generalized Gradient ◽  
Structural Isomers ◽  
Functional Theory ◽  
Ferromagnetic Ground State ◽  
Spin Isomers ◽  
Pseudo Potential

In a recent beam deflecting experiment was found that high and low spin states of pure Fe<sub>n</sub> and Co<sub>n</sub> clusters with <em>n</em> ≤ 300 atoms coexist at cryogenic temperatures. In this work we have studied the high spin (HS) and low spin (LS) states of several structural isomers of Co<sub>23</sub>, Co<sub>34</sub>, Fe<sub>34</sub>, and Fe<sub>40</sub> using the generalized gradient approximation (GGA) to density functional theory as implemented in the first-principles pseudo-potential code SIESTA. The calculated energy difference between these HS and LS isomers is not consistent with the observed coexistence, which can be due to an insufficient account of many body correlation effects in the GGA description, or to unknown isomer structures of these clusters. We have calculated within the same tools the magnetic isomers of Co<sub>12</sub>Cu cluster aimed to re-visit a former DFT prediction of an anti-ferromagnetic ground state. We find, however, a ferromagnetic ground state as expected on physical grounds. Our results exemplify the difficulties of the current DFT approaches to describe the magnetic properties of transition metal systems.

scholarly journals Quantum-Chemical Design of Molecular Structures of Tetra-, Penta- and Hexanuclear Metal Clusters Containing Aluminum and 3d-Element Atoms

Materials ◽  
2020 ◽  
Vol 13 (8) ◽  
pp. 1852
Author(s):  
Oleg V. Mikhailov ◽  
Denis V. Chachkov
Keyword(s):  
Ground State ◽  
Quantum Chemical ◽  
Metal Clusters ◽  
Complex Dynamics ◽  
Thermodynamic Characteristics ◽  
Molecular Structures ◽  
Spin Multiplicity ◽  
Structural Isomers ◽  
The Individual ◽  
The Given

Various data on the structural and thermodynamic characteristics of polynuclear metal clusters containing atoms of aluminum and various d-elements with the general formula AlnMm where (n + m) is 4, 5, or 6, and which can be precursors for the formation of nanoparticles of elemental metals or intermetallic compounds, have been systematized and discussed. It has been noted that each of these metal clusters in principle is able to exist in very diverse structural isomers, differing significantly among themselves in terms of the total energy and spin multiplicity of the ground state, the number of which is determined by both the specific values of n and m, and the nature of d-elements in their compositions. The presence of very complex dynamics with respect to the changes of the individual thermodynamic characteristics of the metal clusters under consideration as well as the thermodynamic parameters of the reactions of their formation, depending on the nature of the d-element, were also ascertained. In the main, the given review is devoted to the authors’ works published over the last 10 years. Bibliography – 96 references.

Structural Isomers of C70

1992 ◽  
Vol 270 ◽  
Author(s):  
Krishnan Raghavachari
Keyword(s):  
Ab Initio ◽  
Ground State ◽  
Quantum Chemical ◽  
Energy Difference ◽  
Structural Isomers ◽  
Chemical Techniques ◽  
Isomeric Structures

ABSTRACTAlternative isomeric structures of C70 have been investigated using semiempirical and ab initio quantum chemical techniques. As in the case of C60, these isomers are characterized by the presence of pentagonal rings adjacent to each other. The lowest energy alternative isomer of C70 has only one pair of edge-sharing pentagons and lies ≈ 1.4 eV higher in energy than the ground state. This energy difference is smaller than that for the lowest energy alternative isomer of C60 which contains two pairs of adjacent pentagons and lies ≈ 2.0 eV higher in energy than its ground state.

Defective Buckyballs: Alternative Structural Isomers of C60

1992 ◽  
Vol 247 ◽  
Author(s):  
Krishnan Raghavachari ◽  
Celeste M. Rohlfing
Keyword(s):  
Ab Initio ◽  
Ground State ◽  
Quantum Chemical ◽  
Structural Isomers ◽  
Chemical Techniques

ABSTRACTAlternative isomerie structures of C60 spheroids have been investigated using semiempirical and ab initio quantum chemical techniques. Unlike the icosahedral ground state, these isomers are characterized by the presence of pentagonal rings adjacent to each other. The lowest energy alternative isomer of C60 has two such pairs of edge-sharing pentagons and lies = 2 eV higher in energy than the ground state. Isomers containing three and four pairs of adjacent pentagons have also been studied in detail. Overall, the energy contributions of these adjacent pentagonal defects are additive, with each defect making the structure less stable by = 1 eV.

Singlet quenching of chlorophyll a and pheophytin a by 2,4,7-trinitro-9-(fluoroenylidene)malononitrile: influence of ground-state complexation

1992 ◽  
Vol 197 (1-2) ◽  
pp. 145-148 ◽  
Author(s):  
L.V. Natarajan ◽  
M.Thandi Buthelezi ◽  
Laura R. Lim ◽  
Raymond Chang
Keyword(s):  
Chlorophyll A ◽  
Ground State ◽  
Pheophytin A

Structural Isomers of the Benzene Dimer from Mass Selective Hole-Burning Spectroscopy

1992 ◽  
Vol 47 (12) ◽  
pp. 1248-1252 ◽  
Author(s):  
W. Scherzer ◽  
O. Krätzschmar ◽  
H. L. Selzle ◽  
E. W. Schlag
Keyword(s):  
Gas Phase ◽  
Ground State ◽  
Supersonic Jet ◽  
Hole Burning ◽  
Structural Isomers ◽  
Benzene Dimer ◽  
Supersonic Jet Expansion

Mass selected hole-burning experiments in the gas phase are presented for the benzene dimer formed in a supersonic jet expansion. The observed spectra show three different ground state configurations for the dimer. From isotopically substituted dimers the structure of the most prominent conformer could be assigned to a very floppy T-shape like structure with two non-equivalent sites for the benzene molecules.

Renilla Bioluminescence: A Morphologic Approach to the Location of Photocytes

1974 ◽  
Vol 32 ◽  
pp. 208-209
Author(s):  
Ben O. Spurlock ◽  
Milton J. Cormier
Keyword(s):  
Excited State ◽  
Ground State ◽  
Molecular Basis ◽  
Light Emission ◽  
Chemical Basis ◽  
Electronic Excited State ◽  
Colonial Form ◽  
The Common ◽  
Eighteenth And Nineteenth Centuries ◽  
Catalyzed Oxidation

The phenomenon of bioluminescence has fascinated layman and scientist alike for many centuries. During the eighteenth and nineteenth centuries a number of observations were reported on the physiology of bioluminescence in Renilla, the common sea pansy. More recently biochemists have directed their attention to the molecular basis of luminosity in this colonial form. These studies have centered primarily on defining the chemical basis for bioluminescence and its control. It is now established that bioluminescence in Renilla arises due to the luciferase-catalyzed oxidation of luciferin. This results in the creation of a product (oxyluciferin) in an electronic excited state. The transition of oxyluciferin from its excited state to the ground state leads to light emission.

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