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Ab Initio Multireference Quantum Chemical Investigations of Molecules: Chemical Bonding, Spectroscopy, and Beyond

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

Deadline for manuscript submissions: 31 December 2025 | Viewed by 977

Special Issue Editor


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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,

Ab initio multireference methods are widely utilized in electronic structure theory. The progression of applying multireference tools for chemical discoveries is attributed to their ability of representing strongly correlated electronic structures of molecular complexes accurately. In many instances, multireference studies are performed for exploring chemical phenomena in spectroscopy, catalysis, and chemical bonding. The application of this level of theory is especially crucial for understanding chemicophysical processes associated with many transition metal-, lanthanide-, and actinide-based systems, owing to their highly correlated electronic structures. Furthermore, due to the high accuracy of multireference theoretical predictions, they are often conjoined with experimental investigations for validating experimental observations as well as tuning and guiding experiments. With today’s easily accessible high-performance computing power, the theoretical multireference investigations of chemical species have accelerated. Hence, aiming to highlight the ongoing multireference quantum chemical efforts in various fields of chemistry and physics, the current Special Issue is established.

Dr. Isuru R. Ariyarathna
Guest Editor

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Keywords

  • quantum chemistry
  • ab initio multireference methods
  • spectroscopy
  • chemical bonding
  • transition metals
  • lanthanides
  • actinides

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Published Papers (2 papers)

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Research

27 pages, 7874 KiB  
Article
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
Viewed by 243
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 [...] Read more.
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, XΣ+6, it is found that Re = 2.708 Å, De = 24.1 kcal/mol, ωe = 316.8 cm1, ωexe = 2.11 cm1, 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 (aΣ+8) to 34.7 (cΠ4), 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 2s2pz hybridization on Li and a 4dz25s5pz or 5s5pz hybridization on Mo are found. Moreover, it is observed that the excited Li(P2) atom forms the shortest bonds because its empty 2s0 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
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20 pages, 5870 KiB  
Article
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
Viewed by 544
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 [...] Read more.
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 1σ21, 1σ21, 1σ21, and 1σ21 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 12Δ3/2, 12Σ+1/2, and 12Δ3/2 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
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