Quantum Chemistry as Applied to Molecular Systems

A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Chemistry: Symmetry/Asymmetry".

Deadline for manuscript submissions: closed (31 March 2024) | Viewed by 7776

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School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
Interests: photophysics; optical spectroscopy; dye chemistry; kinetics; energy and electron transfer; physical chemistry
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Dear Colleagues,

Quantum chemical calculations are an integral part of contemporary chemistry and are used to support experimental work in virtually every part of the discipline. The accuracy of the calculations has improved steadily while the knowledge, tools, and expertise have been passed from specialist to general user. The result has been improved understanding, accelerated discovery, and facilitated optimisation of molecules, molecular materials, and interfaces. This Special Issue seeks to coordinate recent advances in quantum chemical methodology in the general field of molecular science. Emphasis is given to quantum chemical studies of molecular associates, such as dimers, in both ground and excited states and in developing new tools to aid spectroscopic investigations. Both excitonic and vibronic couplings are now addressable by theoretical methods, while the involvement of charge transfer or extended p-conjugation in large organic molecules merits special attention. The study of delocalised organic radicals, such as those derived from cyanine dyes, is necessary for an improved understanding of super-resolution microscopy. Manuscripts covering related topics are welcome.

Prof. Dr. Anthony Harriman
Guest Editor

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Keywords

  • Charge transfer 
  • Excited states
  • Push–pull molecules 
  • Delocalised radicals 
  • Intersystem crossing
  • Quantum confinement in organic molecules
  • Spectroscopy 
  • Circular dichroism
  • Molecular aggregates
  • Excitonic coupling 
  • Vibronic coupling 
  • Excimers 
  • Quantum coherence
  • Circularly polarised luminescence

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Published Papers (3 papers)

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Research

15 pages, 3409 KiB  
Article
Preference of C2v Symmetry in Low-Spin Hexacarbonyls of Rare-Earth and f Elements
by Attila Kovács and Werner Klotzbücher
Symmetry 2024, 16(2), 178; https://doi.org/10.3390/sym16020178 - 2 Feb 2024
Viewed by 1133
Abstract
The structures and bonding of selected neutral M(CO)6 complexes (M = Sc, Y, La, Lu, Ac and U) have been studied by density functional theory calculations. The calculations revealed the preference for C2v symmetry and low-spin electronic state for most of [...] Read more.
The structures and bonding of selected neutral M(CO)6 complexes (M = Sc, Y, La, Lu, Ac and U) have been studied by density functional theory calculations. The calculations revealed the preference for C2v symmetry and low-spin electronic state for most of these complexes. The relative stability of the low-symmetry species increases gradually with the size of the metal atom. While the characteristic Oh hexa-coordinated structure is favored in the high-spin electronic state of the smaller metals, for heavier metals, important advantages of the C2v vs. Oh structures include larger charge transfer interactions in terms of transferred electrons as well as better steric conditions. Our joint experimental–theoretical analysis detected and confirmed the Oh structure of the Sc(CO)6 complex in cryogenic CO/Ar matrices. Full article
(This article belongs to the Special Issue Quantum Chemistry as Applied to Molecular Systems)
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10 pages, 1890 KiB  
Article
The Au12 Gold Cluster: Preference for a Non-Planar Structure
by Pham Vu Nhat, Nguyen Thanh Si, Nguyen Ngoc Khanh Anh, Long Van Duong and Minh Tho Nguyen
Symmetry 2022, 14(8), 1665; https://doi.org/10.3390/sym14081665 - 11 Aug 2022
Cited by 7 | Viewed by 2563
Abstract
The transition point from a two-dimensional (2D) to a three-dimensional (3D) structure in a series of small gold clusters remains a topic of continuing debate. In the present study, coupled-cluster CCSD(T) and DFT calculations are performed to re-examine the relative energies of several [...] Read more.
The transition point from a two-dimensional (2D) to a three-dimensional (3D) structure in a series of small gold clusters remains a topic of continuing debate. In the present study, coupled-cluster CCSD(T) and DFT calculations are performed to re-examine the relative energies of several low-lying isomers of Au12, aiming to shed new light on this issue. At odds with many previous reports on the preference of a planar di-capped elongated-hexagon structure, the Au12 size is found to energetically prefer a globular cup-like form with C2v symmetry. While DFT results are not able to assign the most stable form of Au12 as the relative energies between the lowest-lying isomers are strongly functional-dependent, coupled-cluster theory calculations point out the preference of a 3D structure for having a D3h symmetry. Such a prediction is further supported by a comparison of the vibrational spectra computed using the revTPSS density functional with the available experimental infrared ones that were previously recorded from the far-IR multiple photon dissociation (FIR-MPD) experiment. Full article
(This article belongs to the Special Issue Quantum Chemistry as Applied to Molecular Systems)
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11 pages, 1694 KiB  
Article
The Interplay between Diradical Character and Stability in Organic Molecules
by Vaska Petakova, Miroslava Nedyalkova, Joanna Stoycheva, Alia Tadjer and Julia Romanova
Symmetry 2021, 13(8), 1448; https://doi.org/10.3390/sym13081448 - 7 Aug 2021
Cited by 1 | Viewed by 3103
Abstract
The number of scientific papers on the unique properties and the potential for various applications of compounds with a diradical character is growing constantly. The diradical character enhances and even engenders certain desired optical properties and its modulation is a modern molecular design [...] Read more.
The number of scientific papers on the unique properties and the potential for various applications of compounds with a diradical character is growing constantly. The diradical character enhances and even engenders certain desired optical properties and its modulation is a modern molecular design strategy. Nowadays, molecules with a non-zero diradical character are regarded as promising materials for new-generation and highly efficient solar cells and photonics devices. What is the price, however, of the unique properties of open-shell compounds? Alongside all the benefits, the diradical character is usually associated with low stability and high reactivity—unwanted molecular qualities for practical purposes. Thus, from a fundamental and applied point of view, it is important to investigate the correlation between the diradical character and laboratory stability, which is the goal of the present paper. Here, we report a combined quantum–chemical study (conceptual DFT and spin-projected HF theory) and multivariate analysis of the diradical character of a series of o- and p-quinomethides, for the stability of which experimental data are available. Our results reveal that a compromise between the diradical character and laboratory stability of a molecule is feasible and that the relationship between these two quantities can be understood in the framework of Clar’s sextet theory. Full article
(This article belongs to the Special Issue Quantum Chemistry as Applied to Molecular Systems)
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