Aromaticity in Isoelectronic Analogues of Benzene, Carborazine and Borazine, from Electronic Structure and Magnetic Property.

Carborazine (BCNH) and borazine (BNH) are isoelectronic analogues of benzene (CH). The aromatic character of borazine have basically reached a consensus after a long period of controversy, but the related properties of carborazine are even rarely reported. In this work, we systematically investigated the geometric structure, charge distribution, frontier molecular orbital characteristics, bonding, electronic delocalization, magnetic shielding effect, and induced ring current of carborazine and borazine, and compared the studied characteristics with those of benzene to determine the aromatic character of the two analogues.

A comprehensive electron wavefunction analysis toolbox for chemists, Multiwfn.

Analysis of electron wavefunction is a key component of quantum chemistry investigations and is indispensable for the practical research of many chemical problems. After more than ten years of active development, the wavefunction analysis program Multiwfn has accumulated very rich functions, and its application scope has covered numerous aspects of theoretical chemical research, including charge distribution, chemical bond, electron localization and delocalization, aromaticity, intramolecular and intermolecular interactions, electronic excitation, and response property. This article systematically introduces the features and functions of the latest version of Multiwfn and provides many representative examples.

Theoretical Insight into Complexation Between Cyclocarbons and C Fullerene.

This work conducts a comprehensive theoretical study on the non-covalent complexation between cyclocarbons and C fullerene for the first time. The binding energy between cyclocarbons and C fullerene is significantly stronger than that between two C or two C fullerenes, indicating a particularly strong affinity. The cyclocarbons and C fullerene can spontaneously assemble into complexes in the gas phase at room temperature, and the hydrophobic effect caused by the solvent environment can promote this binding.

Energetic Information from Information-Theoretic Approach in Density Functional Theory as Quantitative Measures of Physicochemical Properties.

The Hohenberg-Kohn theorem of density functional theory (DFT) stipulates that energy is a universal functional of electron density in the ground state, so energy can be thought of having encoded essential information for the density. Based on this, we recently proposed to quantify energetic information within the framework of information-theoretic approach (ITA) of DFT (. , 157, 101103).

Theoretical Prediction and Comprehensive Characterization of an All-Nitrogenatomic Ring, Cyclo[18]Nitrogen (N).

The cyclic molecule cyclo[18]carbon composed of 18 carbon atoms has been observed in condensed phase experiment in recent years and has attracted great attention. Through state-of-art quantum chemistry calculation, this study found that 18 nitrogen atoms can also form a macrocyclic system, cyclo[18]nitrogen (N), though its lifetime is very short at room temperature and can only exist for a relatively long time at very low temperatures. We comprehensively theoretically studied properties of N, including geometric configurations, thermal decomposition mechanism and rate, molecular dynamics behavior, energetic properties, vibrational and electronic spectra.

Exploring the Aromaticity Differences of Isoelectronic Species of Cyclo[18]carbon (C), BCN, and BN: The Role of Carbon Atoms as Connecting Bridges.

The cyclo[18]carbon (C) has piqued widespread interest in recent years for its geometrical aesthetic and unique electronic structure. Inspired by it, theoretical investigations of its isoelectronic BN have been published occasionally; however, few studies considered their other companion BCN. In this work, we study the geometric structure, charge distribution, bonding characteristic, aromaticity, and electron delocalization of BCN and BN for the first time and compare the relevant results with those of C.

Size dependence of optical nonlinearity for H-capped carbon chains, H-(CC)-H ( = 3-15): analysis of its nature and prediction for long chains.

Based on a computational approach that can accurately describe their geometric structures and electronic spectra, we have theoretically studied the nonlinear optical (NLO) properties of H-capped carbon chains, H-(CC)-H ( = 3-15), for the first time. Special attention was paid to the size dependence of the molecular (hyper)polarizability of these species through the nonlinear fitting of the data, which formed two power-law formulas of (∞) = -0.206 + 0.

Simple, Efficient, and Universal Energy Decomposition Analysis Method Based on Dispersion-Corrected Density Functional Theory.

Energy decomposition analysis (EDA) is an important class of methods to explore the nature of interaction between fragments in a chemical system. It can decompose the interaction energy into different physical components to understand the factors that play key roles in the interaction. This work proposes an EDA strategy based on dispersion-corrected density functional theory (DFT), called sobEDA.

Topological analysis of information-theoretic quantities in density functional theory.

We have witnessed considerable research interest in the recent literature about the development and applications of quantities from the information-theoretic approach (ITA) in density functional theory. These ITA quantities are explicit density functionals, whose local distributions in real space are continuous and well-behaved. In this work, we further develop ITA by systematically analyzing the topological behavior of its four representative quantities, Shannon entropy, two forms of Fisher information, and relative Shannon entropy (also called information gain or Kullback-Leibler divergence).

Theoretical design of a dual-motor nanorotator composed of all-carboatomic cyclo[18]carbon and a figure-of-eight carbon hoop.

A novel supramolecular complex (2C@OPP) constructed from two kinds of unique nanorings, all-carboatomic cyclo[18]carbon (C) and figure-of-eight carbon hoop (OPP), has been studied theoretically from the perspective of an extraordinary dual-motor nanorotator. The rotational barrier of C in OPP is extremely small at ambient temperature, implying the possibility of the host-guest complex as an ultrafast nanorotator. The rotational characteristics and thermodynamic stability of the nanorotator at different temperatures were then explored.

Molecular assembly with a figure-of-eight nanohoop as a strategy for the collection and stabilization of cyclo[18]carbon.

The recently synthesized novel figure-of-eight nanohoop with two strained oligoparaphenylenes (OPPs) was theoretically designed to collect and stabilize new allotropic carbon cyclo[18]carbon (C) through molecular assembly. The size adaptability and shape complementarity of C to OPP make it possible for them to combine into extraordinary ring-in-ring supramolecules. Thermodynamic analysis of 2C@OPP showed that the host-guest complex should spontaneously form below 404 K.

Electronic Structure and Aromaticity of an Unusual Cyclo[18]carbon Precursor, C Br.

Herein, the electronic structure and bonding character of the stable cyclo[18]carbon (C ) precursor, C Br , are thoroughly characterized by molecular orbital (MO), density of states (DOS), bond order (BO), and interaction region indicator (IRI) analyses. The delocalization characters of out-of-plane and in-plane π-electrons (labeled as π - and π -electrons, respectively) in bonding regions were examined using localized orbital locator (LOL) and electron localization function (ELF). The aromaticity was investigated, studying the molecular magnetic response to external magnetic field by computing the magnetically induced current density (J ), iso-chemical shielding surface (ICSS), anisotropy of the induced current density (AICD), and the induced magnetic field (B ).

Effects of external field wavelength and solvation on the photophysical property and optical nonlinearity of 1,3-thiazolium-5-thiolates mesoionic compound.

The photophysical property and optical nonlinearity of an electronic push-pull mesoionic compound, 2-(4-trifluoromethophenyl)-3-methyl-4-(4-methoxyphenyl)-1,3-thiazole-5-thiolate, were theoretically investigated with a reliable computing strategy. The essence of the optical properties were then explored through a variety of wavefunction analysis methods, including the natural transition orbital analysis, hole-electron analysis, (hyper)polarizability density analysis, decomposition of the (hyper)polarizability contribution, and (hyper)polarizability tensor analysis, at the level of electronic structure. The influences of the electric field and solvation on the absorption spectrum and (hyper)polarizability of the molecule are highlighted and clarified.

Toward Density-Based and Simultaneous Description of Chemical Bonding and Noncovalent Interactions with Pauli Energy.

Chemical bonds and noncovalent interactions are extraordinarily important concepts in chemistry and beyond. Using density-based quantities to describe them has a long history in the literature, yet none can satisfactorily describe the entire spectrum of interactions from strong chemical bonds to weak van der Waals forces. In this work, employing Pauli energy as the theoretical foundation, we fill in that knowledge gap.

Photophysical properties and optical nonlinearity of cyclo[18]carbon (C) precursors, C-(CO) ( = 2, 4, and 6): focusing on the effect of the carbonyl groups.

The electronic spectra and (hyper)polarizability of C-(CO) ( = 2, 4, and 6) are studied using theoretical calculations to reveal the effect of introducing carbonyl (-CO) groups on the molecular optical properties. Successive introduction of -CO groups is observed to cause a red-shift in the absorption spectrum, but maximum absorption of all molecules is mainly due to the charge redistribution within the C moiety. The (hyper)polarizabilities of the cyclocarbon oxides present an ascending trend with the -CO groups in the molecule, and the higher-order response properties are more sensitive.

Independent gradient model based on Hirshfeld partition: A new method for visual study of interactions in chemical systems.

The powerful independent gradient model (IGM) method has been increasingly popular in visual analysis of intramolecular and intermolecular interactions in recent years. However, we frequently observed that there is an evident shortcoming of IGM map in graphically studying weak interactions, that is its isosurfaces are usually too bulgy; in these cases, not only the graphical effect is poor, but also the color on some areas on the isosurfaces is inappropriate and may lead to erroneous analysis conclusions. In addition, the IGM method was originally proposed based on promolecular density, which is quite crude and does not take actual electronic structure into account.

Bonding Character, Electron Delocalization, and Aromaticity of Cyclo[18]Carbon (C ) Precursors, C -(CO) (n=6, 4, and 2): Focusing on the Effect of Carbonyl (-CO) Groups.

The bonding character, electron delocalization, and aromaticity of the cyclo[18]carbon (C ) precursors, C -(CO) (n=6, 4, and 2), have been studied by combining quantum chemical calculations and various electronic wavefunction analyses with different physical bases. It was found that C -(CO) (n=6, 4, and 2) molecules exhibit alternating long and short C-C bonds, and have out-of-plane and in-plane dual π systems (π and π ) perpendicular to each other, which are consistent with the relevant characteristics of C . However, the presence of carbonyl (-CO) groups significantly reduced the global electron conjugation of C -(CO) (n=6, 4, and 2) compared to C .

Efficient evaluation of electrostatic potential with computerized optimized code.

The evaluation of molecular electrostatic potential (ESP) is a performance bottleneck for many computational chemical tasks like restrained ESP charge fitting or quantum mechanics/molecular mechanics simulations. In this paper, an efficient algorithm for the evaluation of ESP is proposed. It regroups the expression in terms of primitive Gaussian type orbitals (GTOs) with identical angular momentum types and nuclei centers.

Simple, reliable, and universal metrics of molecular planarity.

Planarity is a very important structural character of molecules, which is closely related to many molecular properties. Unfortunately, there is currently no simple, universal, and robust way to measure molecular planarity. In order to fill this evident gap, we propose two metrics of molecular planarity, namely molecular planarity parameter (MPP) and span of deviation from plane (SDP), to quantitatively characterize planarity of molecules.

Remarkable Size Effect on Photophysical and Nonlinear Optical Properties of All-Carboatomic Rings, Cyclo[18]carbon and Its Analogues.

Inspired by recent experimental observation of molecular morphology and theoretical predictions of multiple properties of cyclo[18]carbon, we systematically studied the photophysical and nonlinear optical properties of cyclo[2N]carbons (N=3-15) allotropes through density functional theory. This work unveils the unusual optical properties of the sp-hybridized carbon rings with different sizes. The remarkable size dependence of the optical properties of these systems and their underlying nature are profoundly explored, and the relevance between aromaticity and optical properties are highlighted.

Local Temperature as a Chemical Reactivity Descriptor.

Using the electron density and its associated quantities in a molecular system to quantify chemical reactivity in density functional theory is of considerable recent interest. Local temperature based on the kinetic energy density is an intrinsic property of a molecular system, which can be employed for this purpose. In this work, we explore such a possibility.

Quantifications and Applications of Relative Fisher Information in Density Functional Theory.

Though density functional theory is widely accepted as one of the most successful developments in theoretical chemistry in the past few decades, the knowledge of how to apply this new electronic structure theory, to help us better understand chemical processes and transformations, is still an unaccomplished task. The information-theoretic approach is emerging as a viable option for that purpose in the recent literature, providing new insights about steric effect, cooperativity, electrophilicity, nucleophilicity, stereoselectivity, homochirality, etc. In this work, based on the result from a recent paper by one of us [ , 2019, 151, 141103], we present two quantifications of the relative Fisher information and discuss their physiochemical properties and possible applications.

Comment on "Theoretical investigation on bond and spectrum of cyclo[18]carbon (C) with sp-hybridized".

Recently, Shuhong Xu et al. reported theoretical calculation of molecular structure, bonding, aromaticity, electron delocalization, and electronic spectrum of cyclo[18]carbon in J. Mol.

Ultrastrong Regulation Effect of the Electric Field on the All-Carboatomic Ring Cyclo[18]Carbon*.

Cyclo[18]carbon has a very unique geometry and electronic structure. We found that an external electric field (EEF) has an ultrastrong regulation effect on various aspects of the cyclo[18]carbon: (1) The EEF makes the shape of the cyclo[18]carbon change from a circle to an oval, the elongation is particularly striking at a large EEF magnitude. (2) The EEF causes a huge polarization of distribution of in-plane π electrons, and strong EEF can even make some of the electrons detached from the carbon ring (3) EEF significantly lowers LUMO energy and reduces HOMO-LUMO gap (4) Large EEF leads to absorption band in the visible light range and thus makes the cyclo[18]carbon display color (5) Strong EEF causes a large number of new absorption peaks in IR spectrum.