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.

Quantum-Chemical Ab Initio Calculations on Inda- and Thallabenzene (C5H5In and C5H5Tl) and their Structural Isomers η5-C5H5In and η5-C5H5Tl

2018 ◽  
Vol 71 (3) ◽  
pp. 102
Author(s):  
Emma Persoon ◽  
Yuekui Wang ◽  
Gerhard Raabe
Keyword(s):  
Ab Initio ◽  
Quantum Chemical ◽  
Density Functional ◽  
Single Point ◽  
Normal Modes ◽  
Dft Method ◽  
Basis Sets ◽  
Triplet States ◽  
Structural Isomers ◽  
Td Dft

Quantum-chemical ab initio, time-independent, as well as time-dependent density functional theory (TD-DFT) calculations were performed on the so far elusive heterocycles inda- and thallabenzene (C5H5In and C5H5Tl), employing several different methods (MP2, CISD, CCSD, CCSD(T), BD, BD(T), QCISD, QCISD(T), CASSCF, DFT/B3LYP), effective core potentials, and different basis sets. While calculations on the MP2 level predict the ground states of the title compounds to be singlets with the first triplet states between 13 and 15 kcal mol−1 higher in energy, single point calculations with the QCISD(T), CCSD(T), and BD(T) methods at CCSD-optimized structures result in energy differences between the singlet and the triplet states in the range between 0.3 and 2.1 kcal mol−1 in favour of the triplet states. According to a CASSCF(8,8) calculation the triplets are also more stable by about 2.5–2.9 kcal mol−1. Calculations were also performed for the C5v-symmetric η5 structural isomers (cyclopentadienylindium, CpIn, and cyclopentadienylthallium, CpTl, Cp = C5H5) of the title compounds. At the highest level of theory employed in this study, C5H5In is between 79 and 88 kcal mol−1 higher in energy than CpIn, while this energy difference is even larger for thallabenzene where C5H5Tl is energetically between 94 and 102 kcal mol−1 above CpTl. In addition we report on the UV/vis spectra calculated with a TD-DFT method as well as on the spectra of the normal modes of C5H5In and C5H5Tl. Both types of spectra might facilitate identification of the title compounds eventually formed in photolysis or pyrolysis experiments.

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 Theoretical Simulation of the Zeke Spectra of Naphthalene From Single Vibronic Levels of S1

1999 ◽  
Vol 19 (1-4) ◽  
pp. 105-108 ◽  
Author(s):  
Fabrizia Negri ◽  
Marek Z. Zgierski
Keyword(s):  
Ab Initio ◽  
Quantum Chemical Calculations ◽  
Ground State ◽  
Quantum Chemical ◽  
Electronic States ◽  
Perturbative Expansion ◽  
Molecular Structures ◽  
Theoretical Simulation ◽  
Vibronic States ◽  
Semi Empirical

We present the simulations and analysis of the two-color ZEKE spectra of naphthalene, performed with the help of quantum chemical calculations of molecular parameters followed by the modelling of vibronic intensities. Ab initio and semi-empirical calculations were carried out to obtain molecular structures of neutral and ionic naphthalene, and vibronic perturbations that couple the electronic states. It is shown that the intensities, simulated with a model based on the perturbative expansion of vibronic states, nicely reproduce the observed spectra and contribute to reassign some of the ground state frequencies of naphthalene cation.

The anomalous gas phase acidity of ethyl fluoride. An abinitio investigation of the importance of hydrogen bonding between F− and sp2 and sp C—H bonds

1985 ◽  
Vol 63 (3) ◽  
pp. 708-715 ◽  
Author(s):  
M. Roy ◽  
T. B. McMahon
Keyword(s):  
Gas Phase ◽  
Quantum Chemical ◽  
Molecular Formula ◽  
Stable Isomer ◽  
Structural Isomers ◽  
Proton Abstraction ◽  
Gas Phase Acidity ◽  
Chemical Techniques ◽  
Gas Phase Ion ◽  
Hydrogen Bonded

Abinitio quantum chemical techniques have been used to investigate the structures and energetics of a number of hydrogen bonded adducts of F− and C—H bonds associated with unsaturated systems as well as their structural isomers. Examination of the possible species of molecular formula C2H4F− reveals that the most stable isomer is a hydrogen bonded adduct of F− and ethylene, while the classical β-fluoroethyl carbanion is found not to be bound with respect to dissociation into F− + C2H4. Similar examination of C2H2F− isomers shows that a hydrogen bonded F−–acetylene adduct is the most stable structure, however, the remaining α and β-fluorovinyl carbanions are found to be bound with respect to F− + C2H2. These results are used to explain the unusual gas phase acidities of ethylfluoride and vinylfluoride. Calculations on C3H4F− isomers show the hydrogen bonded adduct of F− and allene to be more stable than the classical 2-fluoropropenyl anion and on C2H2FO− isomers show the enolate of acetyl fluoride to be more stable than the hydrogen bonded adduct of F− and ketene. These latter results are used to explain the gas phase ion molecule reactivities of C3H4F− (predominantly F− transfer) and C2H2FO− (proton abstraction).

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.

scholarly journals Quantum-Chemical ab initio Calculations on the Three Isomers of Diborabenzene (C4H4B2)

2010 ◽  
Vol 65 (1-2) ◽  
pp. 113-122 ◽  
Author(s):  
Jaswinder Singh ◽  
Yuekui Wang ◽  
Gerhard Raabe
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Quantum Chemical ◽  
Ground States ◽  
Closed Shell ◽  
Triplet States ◽  
Structural Isomers ◽  
Carbon Carbon Bond ◽  
Lowest Unoccupied Molecular Orbitals ◽  
Effective Stabilization

AbstractQuantum-chemical ab initio calculations up to the ZPE+CCSD(T)/aug-cc-pVTZ//MP2/6- 311++G** level were performed on three possible structural isomers of diborabenzene (C4H4B2). All three molecules were found to be local minima on the C4H4B2 energy surface and to have closed shell singlet ground states. While the ground states of the 1,3- and 1,4-isomer are planar and of C2v and D2h symmetry, respectively, 1,2-diborabenzene is non-planar with a C2 axis passing through the center of the BB bond and the middle of the opposite carbon-carbon bond as the only symmetry element. The energetically most favourable 1,3-diborabenzene was found to be about 19 and 36 kcal/mol lower in energy than the 1,2- and the 1,4-isomer. Planar 1,3- and 1,4-diborabenzene have three doubly occupied π orbitals while non-planar 1,2-diborabenzene has also three doubly occupied orbitals which can be derived from the π orbitals of its 3.7 kcal/mol energetically less favourable planar form (“π-like” orbitals). The lowest unoccupied orbitals of all three isomers have σ symmetry with large coefficients at the two boron atoms. These orbitals are lower in energy than the lowest unoccupied molecular orbitals (LUMOs) of e. g. benzene and pyridine and might cause pronounced acceptor properties which could be one of the reasons for the elusiveness of the title compounds. The results of bond separation reactions show that cyclic conjugation stabilizes all three diborabenzenes relative to their isolated fragments. The most effective stabilization energy of about 24 kcal/mol was found for the energetically lowest 1,3-isomer. This value amounts to approximately one third of the experimental value for the bond separation energy of pyridine. In all cases the energetically lowest triplet states are significantly (16 - 24 kcal/mol) higher in energy than the singlet ground states. Also among the triplets the 1,3-isomer is the energetically most fabourable species.

Evaluation of Chemotherapeutic Activity of the Selected Bases’ Analogues of Nucleic Acids Supported by ab initio Various Quantum Chemical Calculations

2020 ◽  
Vol 16 (2) ◽  
pp. 93-103 ◽  
Author(s):  
Piotr Kawczak ◽  
Leszek Bober ◽  
Tomasz Bączek
Keyword(s):  
Biological Activity ◽  
Nucleic Acids ◽  
Ab Initio ◽  
Quantum Chemical Calculations ◽  
Quantum Chemical ◽  
Structural Parameters ◽  
Principal Component ◽  
Polarizable Continuum Model ◽  
Activity Data ◽  
Qsar Models

Background: Pharmacological and physicochemical classification of bases’ selected analogues of nucleic acids is proposed in the study. Objective: Structural parameters received by the PCM (Polarizable Continuum Model) with several types of calculation methods for the structures in vacuo and in the aquatic environment together with the huge set of extra molecular descriptors obtained by the professional software and literature values of biological activity were used to search the relationships. Methods: Principal Component Analysis (PCA) together with Factor Analysis (FA) and Multiple Linear Regressions (MLR) as the types of the chemometric approach based on semi-empirical ab initio molecular modeling studies were performed. Results: The equations with statistically significant descriptors were proposed to demonstrate both the common and differentiating characteristics of the bases' analogues of nucleic acids based on the quantum chemical calculations and biological activity data. Conclusion: The obtained QSAR models can be used for predicting and explaining the activity of studied molecules.

Quantum chemical prediction of 2H-pyran vibration spectrum

1990 ◽  
Vol 55 (1) ◽  
pp. 10-20 ◽  
Author(s):  
Stanislav Böhm ◽  
Josef Kuthan
Keyword(s):  
Vibrational Spectrum ◽  
Ab Initio ◽  
Quantum Chemical ◽  
Vibration Spectrum ◽  
Equilibrium Geometry ◽  
Heterocyclic Molecule ◽  
Vibrational Transitions ◽  
Correlation Corrections

Ab initio MO optimalization of the 2H-pyran molecule leads to a defined equilibrium geometry of this so far not identified heterocyclic molecule and to a physical justification of its existence. More advanced nonempirical wavefunctions and temperature corrections indicate that heterocyclic molecule I is energetically less stable than non-cyclic isomers II and III. Wavenumbers of fundamental vibrational transitions of heterocycle I and also known (2E)-2,4-pentadienal (IIIb were calculated using 3-21 G wavefunctions. The vibrational spectrum of compound I is predicted on the basis of correlation corrections.

Sign in / Sign up

Export Citation Format

Share Document