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17 pages, 1323 KB

Open AccessArticle

Predicting the Post-Hartree-Fock Electron Correlation Energy of Complex Systems with the Information-Theoretic Approach

by Ping Wang, Dongxiong Hu, Linling Lu, Yilin Zhao, Jingbo Chen, Paul W. Ayers, Shubin Liu and Dongbo Zhao

Molecules 2025, 30(17), 3500; https://doi.org/10.3390/molecules30173500 - 26 Aug 2025

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Abstract

Employing some simple physics-inspired density-based information-theoretic approach (ITA) quantities to predict the electron correlation energies remains an open challenge. In this work, we expand the scope of the LR(ITA) (LR means linear regression) protocol to more complex systems, including (i) 24 octane isomers; (ii) polymeric structures, polyyne, polyene, all-trans-polymethineimine, and acene; (iii) molecular clusters, such as metallic Be_n and Mg_n, covalent S_n, hydrogen-bonded protonated water clusters H⁺(H₂O)_n, and dispersion-bound carbon dioxide (CO₂)_n, and benzene (C₆H₆)_n clusters. With LR(ITA), one can simply predict the post-Hartree-Fock (such as MP2 and coupled cluster) electron correlation energies at the cost of Hartree-Fock calculations, even with chemical accuracy. For large molecular clusters, we employ the linear-scaling generalized energy-based fragmentation (GEBF) method to gauge the accuracy of LR(ITA). Employing benzene clusters as an illustration, the LR(ITA) method shows similar accuracy to that of GEBF. Overall, we have verified that ITA quantities can be used to predict the post-Hartree-Fock electron correlation energies of various complex systems. Full article

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13 pages, 431 KB

Open AccessArticle

Effect of Oriented External Electric Fields on the Electronic Properties of Linear Acenes: A Thermally Assisted Occupation DFT Study

by Chi-Yu Chen and Jeng-Da Chai

Molecules 2024, 29(17), 4245; https://doi.org/10.3390/molecules29174245 - 6 Sep 2024

Cited by 2 | Viewed by 1475

Abstract

Recently, oriented external electric fields (OEEFs) have earned much attention due to the possibility of tuning the properties of electronic systems. From a theoretical perspective, one can resort to electronic structure calculations to understand how the direction and strength of OEEFs affect the properties of electronic systems. However, for multi-reference (MR) systems, calculations employing the popular Kohn–Sham density functional theory with the traditional semilocal and hybrid exchange–correlation energy functionals can yield erroneous results. Owing to its decent compromise between accuracy and efficiency for MR systems at the nanoscale (i.e., MR nanosystems), in this study, thermally assisted occupation density functional theory (TAO-DFT) is adopted to explore the electronic properties of n-acenes (n = 2–10), containing n linearly fused benzene rings, in OEEFs, where the OEEFs of various electric field strengths are applied along the long axes of n-acenes. According to our TAO-DFT calculations, the ground states of n-acenes in OEEFs are singlets for all the cases examined. The effect of OEEFs is shown to be significant on the vertical ionization potentials and vertical electron affinities of ground-state n-acenes with odd-number fused benzene rings. Moreover, the MR character of ground-state n-acenes in OEEFs increases with the increase in the acene length and/or the electric field strength. Full article

(This article belongs to the Special Issue Multiconfigurational and DFT Methods Applied to Chemical Systems—2nd Edition)

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15 pages, 595 KB

Open AccessArticle

TAO-DFT with the Polarizable Continuum Model

by Sonai Seenithurai and Jeng-Da Chai

Nanomaterials 2023, 13(10), 1593; https://doi.org/10.3390/nano13101593 - 10 May 2023

Cited by 8 | Viewed by 3015

Abstract

For the ground-state properties of gas-phase nanomolecules with multi-reference character, thermally assisted occupation (TAO) density functional theory (DFT) has recently been found to outperform the widely used Kohn–Sham DFT when traditional exchange-correlation energy functionals are employed. Aiming to explore solvation effects on the ground-state properties of nanomolecules with multi-reference character at a minimal computational cost, we combined TAO-DFT with the PCM (polarizable continuum model). In order to show its usefulness, TAO-DFT-based PCM (TAO-PCM) was used to predict the electronic properties of linear acenes in three different solvents (toluene, chlorobenzene, and water). According to TAO-PCM, in the presence of these solvents, the smaller acenes should have nonradical character, and the larger ones should have increasing polyradical character, revealing striking similarities to the past findings in the gas phase. Full article

(This article belongs to the Special Issue Electronic Properties of 2D/1D Materials and Their Junctions)

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17 pages, 1954 KB

Open AccessArticle

Impact of Di- and Poly-Radical Characters on the Relative Energy of the Doubly Excited and

L_{a}

States of Linear Acenes and Cyclacenes

by Yasi Dai, Juan-Carlos Sancho-García and Fabrizia Negri

Chemistry 2023, 5(1), 616-632; https://doi.org/10.3390/chemistry5010044 - 11 Mar 2023

Cited by 4 | Viewed by 2804

Abstract

Linear and cyclic acenes are polycyclic aromatic hydrocarbons that can be viewed as building blocks of graphene nanoribbons and carbon nanotubes, respectively. While short linear acenes demonstrated remarkable efficiency in several optoelectronic applications, the longer members are unstable and difficult to synthesize as their cyclic counterparts. Recent progress in on-surface synthesis, a powerful tool to prepare highly reactive species, opens promising perspectives and motivates the computational investigations of these potentially functional molecules. Owing to their di- and poly-radical character, low-lying excited states dominated by doubly excited configurations are expected to become more important for longer members of both linear and cyclic molecules. In this work, we investigate the lowest-lying

L_{a}

and the doubly excited (DE) state of linear acenes and cyclacenes, with different computational approaches, to assess the influence of the di-/poly-radical characters (increasing with the molecular dimensions) on their relative order. We show that DFT/MRCI calculations correctly reproduce the crossing of the two states for longer linear acenes, while TDUDFT calculations fail to predict the correct excitation energy trend of the DE state. The study suggests a similarity in the excited electronic state pattern of long linear and cyclic acenes leading ultimately to a lowest lying dark DE state for both. Full article

(This article belongs to the Section Theoretical and Computational Chemistry)

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11 pages, 5960 KB

Open AccessArticle

The Magnetic Response of Starphenes

by Mesías Orozco-Ic and Gabriel Merino

Chemistry 2021, 3(4), 1381-1391; https://doi.org/10.3390/chemistry3040099 - 20 Nov 2021

Cited by 10 | Viewed by 4020

Abstract

The aromaticity of [n]starphenes (n = 1, 4, 7, 10, 13, 16), as well as starphene-based [19]dendriphene, is addressed by calculating the magnetically induced current density and the induced magnetic field, using the pseudo-π model. When an external magnetic field is applied, these systems create diatropic currents that split into a global peripheral current surrounding the starphene skeleton and several local currents in the acene-based arms, resulting in large shielding cones above the arms. In particular, the arm currents are smaller than their linear analogs, and in general, the strengths of the ring currents tend to weaken as the starphene get larger. Full article

(This article belongs to the Special Issue Current Density and Spectroscopy—A Themed Issue in Honor of Professor Riccardo Zanasi on the Occasion of His 70th Birthday)

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14 pages, 2786 KB

Open AccessFeature PaperArticle

Spin Crossover in Bipyridine Derivative Bridged One-Dimensional Iron(III) Coordination Polymer

by Ryuta Ishikawa, Takeshi Noda, Shunya Ueno, Takashi Okubo, Hirofumi Yamakawa, Ken-ichi Sakamoto and Satoshi Kawata

Magnetochemistry 2020, 6(3), 29; https://doi.org/10.3390/magnetochemistry6030029 - 1 Jul 2020

Cited by 7 | Viewed by 4283

Abstract

Herein, the syntheses, solid-state molecular structures, and characterization of two types of one-dimensional Fe^III coordination polymers showing thermally induced spin crossover are reported. The reaction of [Fe(acen)Cl] (acen²⁻ = N,N′-ethylenebis(acetylacetonylideneaminate) with 3,3′-bpy or 4,4′-bpy (bpy = bipyridine) produced zigzag and linear one-dimensional chain complexes, [Fe(acen)(3,3′-bpy)][BPh₄] (1) or [NEt₃H][Fe(acen)(4,4′-bpy)][BPh₄]₂·0.5(4,4′-bpy) (2), respectively, as confirmed by single crystal X-ray diffraction analysis. Variable-temperature single crystal X-ray diffraction measurements, continuous-wave X-band electron paramagnetic resonance (EPR) spectra, ⁵⁷Fe Mössßauer spectra, and DC magnetic susceptibility data revealed that complex 1 exhibited a gradual and complete spin crossover at a transition temperature of 212 K, while complex 2 undergoes an incomplete spin crossover even at 400 K. Full article

(This article belongs to the Special Issue Stimuli-Responsive Magnetic Molecular Materials)

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