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Quantum Chemistry in Modern Science: Chemical Bonding, Spectroscopy, and Beyond

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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Computational and Theoretical Chemistry".

Deadline for manuscript submissions: 31 January 2027 | Viewed by 4812

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Dr. Isuru R. Ariyarathna

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Guest Editor

Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
Interests: quantum chemistry; excited-state chemistry; chemical bonding; solvated electrons; chemistry of lanthanides and actinides; spectroscopy

Special Issue Information

Dear Colleagues,

Quantum chemical investigations are essential for advancing the field of chemistry. In particular, the development and application of high-level quantum chemical methods—ranging from highly accurate multireference and coupled-cluster approaches to density functional theory—provide critical insight into the electronic structure of molecular systems. The expensive multireference methods are important for exploring chemical phenomena related to spectroscopy, catalysis, and chemical bonding. Their application is crucial for understanding the complex chemicophysical processes associated with transition metal, lanthanide, and actinide systems, which often exhibit strongly correlated electronic structures. Moreover, because of their high predictive accuracy, multireference theoretical approaches are frequently combined with experimental investigations to validate observations, interpret results, and guide the design of new experiments. Coupled-cluster methods, meanwhile, are widely employed to obtain highly accurate properties of single-reference electronic states, whereas single-reference density functional theory remains one of the most practical and broadly used approaches for predicting the properties of large molecular systems with reasonable accuracy. With the increasing accessibility of high-performance computing resources, quantum chemical investigations of chemical systems have accelerated significantly. In light of these advances and to highlight ongoing quantum chemical efforts across diverse areas of chemistry and physics, this Special Issue has been established.

Dr. Isuru R. Ariyarathna
Guest Editor

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Keywords

quantum chemistry
ab initio multireference methods
coupled-cluster
density functional theory
spectroscopy
chemical bonding
transition metals
lanthanides
actinides

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Published Papers (4 papers)

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Research

18 pages, 5369 KB

Open AccessArticle

Study on Thermal Stability, Phase Transition Characteristics, and Pyrolysis Product Distributions of Long-Chain n-Alkanes (C12–C15)

by Zengbo Ke, Yang Zhan, Mei Bai, Fengying Chen and Chengfang Qiao

Molecules 2026, 31(13), 2291; https://doi.org/10.3390/molecules31132291 - 1 Jul 2026

Viewed by 257

Abstract

This study employs a multiscale theoretical approach to systematically investigate the thermal stability, phase transition characteristics, and pyrolysis product distributions of four long-chain n-alkanes ranging from n-dodecane to n-pentadecane (C12–C15). At the electronic structure level, density functional theory calculations reveal that with increasing chain length, the HOMO–LUMO gap narrows monotonically from 8.87 eV to 8.77 eV and global softness increases, indicating enhanced electronic responsiveness to thermal perturbation. Molecular electrostatic potential analysis shows decreasing surface potential variance and 100% nonpolar surface area across all species, confirming that intermolecular interactions are exclusively governed by London dispersion forces. At the condensed-phase level, semiempirical quantum-based molecular dynamics (xTB-MD) simulations at 3500 K over 6 ps trajectories reveal qualitative chain-length-dependent initial bond-breaking patterns: C2 species appear prominently among early fragments for C12–C15 systems, with medium-sized fragments (C3, C4) becoming increasingly prevalent and C1 species relatively less prominent as chain length grows. This work provides an integrated “electronic structure-condensed phase transition-pyrolysis kinetics” perspective, offering precise theoretical insights and critical benchmark data for the pyrolysis mechanisms of long-chain n-alkanes. Full article

(This article belongs to the Special Issue Quantum Chemistry in Modern Science: Chemical Bonding, Spectroscopy, and Beyond)

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14 pages, 2350 KB

Open AccessFeature PaperArticle

Electronic Structure, Ligand Effects, and Chemical Reactivity of the Ground and Low-Lying Excited Electronic States of NpO³⁺

by Taylor Gregory and Evangelos Miliordos

Molecules 2026, 31(8), 1258; https://doi.org/10.3390/molecules31081258 - 10 Apr 2026

Viewed by 822

Abstract

Multi-reference and density functional theory calculations are performed for the diatomic and ligated NpO³⁺ species. The main goal of this study is to provide insights into the stability of the experimentally synthesized N(CH₂CH₂NR)₃NpO (R = SiⁱPr₃) coordination complex and probe its use as a catalyst for the oxidation of methane. The constructed potential energy curves for NpO³⁺ showed the presence of three different types of minima (Np³⁺O, Np⁴⁺O⁻, Np⁵⁺O²⁻) depending on the neptunium–oxygen distance. All these minima are higher in energy than the Np²⁺ + O⁺ fragments, and the more stable Np⁵⁺O²⁻ form is stabilized only due to the presence of the negatively charged -CH₂NR⁻ moiety of the ligand. The C–H bond activation of methane was found to be possible only for the first quintet state of the complex which lies about 30 kcal/mol higher than the ground triplet state. Full article

(This article belongs to the Special Issue Quantum Chemistry in Modern Science: Chemical Bonding, Spectroscopy, and Beyond)

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27 pages, 7874 KB

Open AccessArticle

Electronic Structure of the Ground and Low-Lying States of MoLi

by Constantinos Demetriou and Demeter Tzeli

Molecules 2025, 30(13), 2874; https://doi.org/10.3390/molecules30132874 - 6 Jul 2025

Cited by 1 | Viewed by 1456

Abstract

Molybdenum lithium compounds and materials are being researched and applied in cutting-edge industries; however, their bonding has not been explored in a systematic way. The present study investigates the MoLi molecule, to shed light on its bonding. Specifically, the electronic structure and bonding of the ground and 40 low-lying states of the MoLi molecule are explored, employing multireference methodologies, i.e., CASSCF and MRCISD(+Q) in conjunction with the aug-cc-pV5z(-PP) basis set. Bond distances, dissociation energies, dipole moments as well as common spectroscopic constants are given, while the potential energy curves are plotted. For the ground state, X

{}^{6}Σ_{+}

, it is found that

R_{e}

= 2.708 Å,

D_{e}

= 24.1 kcal/mol,

ω_{e}

= 316.8

{cm}^{- 1}

ω_{e} x_{e}

= 2.11

{cm}^{- 1}

, and μ = 3.63 D. Overall, the calculated states present a variety of bonds, from weak van der Waals up to the formation of 2.5 bonds. The dissociation energies of the calculated states range from 2.3 kcal/mol (

a {}^{8}{Σ^{+}}

) to 34.7 (

c {}^{4}Π

), while the bond distances range from 2.513 Å to 3.354 Å. Finally, dipole moment values up to 3.72 D are calculated. In most states, a 2s

{2 p}_{z}

hybridization on Li and a

{4 d}_{z^{2}}

{5 p}_{z}

or 5s

{5 p}_{z}

hybridization on Mo are found. Moreover, it is observed that the excited Li(

{}^{2}P

) atom forms the shortest bonds because its empty

{2 s}^{0}

orbital can easily accept electrons, resulting in a strong σ dative bond. Finally, the present work highlights the exceptional ability of lithium atoms to participate in a variety of bonding schemes, and it could provide the opening gate for further investigation of this species or associated material and complexes. Full article

(This article belongs to the Special Issue Quantum Chemistry in Modern Science: Chemical Bonding, Spectroscopy, and Beyond)

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20 pages, 5870 KB

Open AccessArticle

An Ab Initio Electronic Structure Investigation of the Ground and Excited States of ScH⁺, YH⁺, and LaH⁺

by Isuru R. Ariyarathna

Molecules 2025, 30(11), 2435; https://doi.org/10.3390/molecules30112435 - 2 Jun 2025

Cited by 4 | Viewed by 1539

Abstract

Multireference configuration interaction (MRCI), Davidson-corrected MRCI (MRCI+Q), coupled-cluster singles, doubles, and perturbative triples [CCSD(T)], and frozen-core full configuration interaction (fcFCI) calculations were carried out using large, correlation-consistent basis sets to investigate the excited states of the Sc atom and the spin–free and spin–orbit coupled potential energy profiles, energetics, spectroscopic constants, and electron populations of low-lying states of MH⁺ (M = Sc, Y, La). The core electron correlation effects, complete basis set effects, and spin–orbit coupling effects were also evaluated. The first four electronic states of all MH⁺ are 1²Δ, 1²Σ⁺, 1²Π, and 2²Σ⁺ with 1σ²1δ¹, 1σ²2σ¹, 1σ²1π¹, and 1σ²3σ¹ single-reference electron configurations, respectively. These states of MH⁺ can be represented by the M²⁺H^– ionic structure. The ground states of ScH⁺, YH⁺, and LaH⁺ are 1²Δ_3/2, 1²Σ⁺_1/2, and 1²Δ_3/2 with 55.45, 60.54, and 62.34 kcal/mol bond energies, respectively. The core electron correlation was found to be vital for gaining accurate predictions on the ground and excited state properties of MH⁺. The spin–orbit coupling effects are minor for ScH⁺ but become substantial moving to YH⁺ and LaH⁺. Overall, the results of this work are in good agreement with the limited set of experimental findings of MH⁺ available in the literature and will be of use for future investigations. Furthermore, the theoretical approaches, findings, and trends reported here are expected to aid studies of similar species. Full article

(This article belongs to the Special Issue Quantum Chemistry in Modern Science: Chemical Bonding, Spectroscopy, and Beyond)

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