Evaluation of the quasi correlated tight-binding (QCTB) model for describing polyradical character in polycyclic hydrocarbons

Luzanov, A. V.; Plasser, Felix; Das, Anita; Lischka, Hans

doi:10.1063/1.4975196

Cited by 24 publications

(21 citation statements)

References 68 publications

(114 reference statements)

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“…This is analogous to the widely used practice of considering the non-idempotency (or non-duodempotency) of the ground state density matrix to measure deviations from Hartree-Fock theory and, thus, unpaired electrons. [110][111][112][113][114][115] To put the equation into a memorable form, we introduce the electron-hole permutation operator P he , which by acting on the 1TDM exchanges the coordinates of the hole and electron, i.e.…”

Section: Classification Of Excited States and Validity Of The Modelsmentioning

confidence: 99%

Toward an understanding of electronic excitation energies beyond the molecular orbital picture

Kimber

Plasser

2020

Phys. Chem. Chem. Phys.

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137

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Section: Classification Of Excited States and Validity Of The Modelsmentioning

confidence: 99%

Toward an understanding of electronic excitation energies beyond the molecular orbital picture

Kimber

Plasser

2020

Phys. Chem. Chem. Phys.

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137

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“…The first system, C 154 , Fig. 3 is related to the periacene -type nanographenes which we discussed previously in Refs [14,17,18]. The second (C 192 ) is the antidote structure taken from Ref.…”

Section: Large Graphene-like Moleculesmentioning

confidence: 98%

“…QCTB [17,18] is based on a crude description of -electron systems by using the alternant MO (AMO) theory. The Devison-Amos model [27] (see also Ref.…”

Section: Local Aromaticity For Singlet Open-shell and Electron Correlmentioning

confidence: 99%

Cyclic Aromaticity within Huckel and Quasi-Correlated Huckel-like Models

Luzanov

2018

Chemical Series

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The paper deals with quantifying aromaticity in π-electron networks by unsophisticated MO techniques. The focus is placed on local aromaticity measures associated with individual benzenoid rings. We revised the ring aromaticity index due to Cioslowski et al (2007) by including explicitly net charges and electron unpairing effects. Our previously introduced quasi-correlated tight-binding (QCTB) approximation serves here as an easily available tool for taking account of π-electron correlations. The latter crucially influence the behavior of large and even small conjugated π-structures with a nontrivial topology. Numerical applications of Hückel and QCTB models to measuring local aromaticity are reported for various structural classes (polycyclic aromatic hydrocarbons (PAHs), graphene nanoflakes, and others). We analytically investigate the aromaticity in conjugated monocycles CNHN (neutral and charged ones). Furthermore, in the same manner several PAH structures (oligocenes, pyrene, perylene, etc.) are considered in their charged states, and the results are compared with those of related quinoid-type systems, such as p-diphenoquinodimethane. It is shown that, unlike usual PAHs, quinodimethane structures tend to increase their aromaticity in dicationic (dianionic) form. In our studies of nanographene aromaticity we find a decrease of the local aromaticity as we move to a center of graphene structures, that is in a sharp contrast to the predictions of NICS (nucleus independent chemical shift), a rather criticized approach. A particular emphasis is being put on measuring local aromaticity in highly correlated π-systems. Typical non-Kekule hydrocarbons (e.g., triangulene radical and polyradicals), are also studied within QCTB by which characteristic difficulties caused by the occurrence of many non-bonding π-MOs, are simply obviated.

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“…One of the areas in which the HMO density matrix has found new grounds of interesting applications is in the diagnostic of radicaloid states in formally closed-shell molecules. In particular, the quasi-correlated tight-binding (QCTB) model quantifies the number of unpaired electrons and the distribution of effectively unpaired electrons (EUE) over the molecule [24][25][26]. The theory has been successfully applied to polycyclic aromatic hydrocarbons and graphene-like molecules.…”

Section: Quasi-correlated Tight-binding Modelmentioning

confidence: 99%

“…The theory has been successfully applied to polycyclic aromatic hydrocarbons and graphene-like molecules. Here we follow [26] in presenting this theory. The QCTB is based on a modification of the HMO Hamiltonian of bipartite molecules in the following way.…”

Section: Quasi-correlated Tight-binding Modelmentioning

confidence: 99%

The electron density function of the Hückel (tight-binding) model

Estrada

2018

Proc. R. Soc. A.

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The Hückel (tight-binding) molecular orbital (HMO) method has found many applications in the chemistry of alternant conjugated molecules, such as polycyclic aromatic hydrocarbons (PAHs), fullerenes and graphene-like molecules, as well as in solid-state physics. In this paper, we found analytical expressions for the electron density matrix of the HMO method in terms of odd-powers of its Hamiltonian. We prove that the HMO density matrix induces an embedding of a molecule into a high-dimensional Euclidean space in which the separation between the atoms scales very well with the bond lengths of PAHs. We extend our approach to describe a quasi-correlated tight-binding model, which quantifies the number of unpaired electrons and the distribution of effectively unpaired electrons. In this case, we found that the corresponding density matrices induce embedding of the molecules into high-dimensional Euclidean spheres where the separation between the atoms contains information about the spin–spin repulsion between them. Using our approach, we found an analytic expression which explains the bond length alternation in polyenes inside the HMO framework. We also found that spin–spin interaction explains the alternation of distances between pairs of atoms separated by two bonds in conjugated molecules.

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Evaluation of the quasi correlated tight-binding (QCTB) model for describing polyradical character in polycyclic hydrocarbons

Cited by 24 publications

References 68 publications

Toward an understanding of electronic excitation energies beyond the molecular orbital picture

Toward an understanding of electronic excitation energies beyond the molecular orbital picture

Cyclic Aromaticity within Huckel and Quasi-Correlated Huckel-like Models

The electron density function of the Hückel (tight-binding) model

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