Vibrational Spectra and Molecular Vibrational Behaviors of All-Carboatomic Rings, cyclo[18]carbon and Its Analogues.

The vibrational spectra of cyclo[18]carbon and its analogues, cyclo[2n]carbon (n=3 to 15), were carefully simulated and characterized. The in-plane C-C stretching vibrations shows strong rigidity, while out-of-plane motions seem to be extremely flexible. The solvation effect can enhance signal strengths of the vibrational spectra, but does not evidently change the shape of the spectral curves.

van der Waals potential: an important complement to molecular electrostatic potential in studying intermolecular interactions.

Electrostatics and van der Waals (vdW) interactions are two major components of intermolecular weak interactions. Electrostatic potential has been a very popular function in revealing electrostatic interaction between the system under study and other species, while the role of vdW potential was less recognized and has long been ignored. In this paper, we explicitly present definition of vdW potential, describe its implementation details, and demonstrate its important practical values by several examples.

Molecular dynamics simulations on fullerene surfactants with different charges at the air-water interface.

The interfacial activity of fullerene surfactants at the air-water interface is studied via molecular dynamics and metadynamics simulations. Fullerene surfactants with different charges show different surface activity. Meanwhile, studies show that fullerene surfactants with zero or one positive charge show interesting interface behaviour, i.

Theoretical Framework of 1,3-Thiazolium-5-Thiolates Mesoionic Compounds: Exploring the Nature of Photophysical Property and Molecular Nonlinearity.

Inspired by a previous experimental study on the first-order hyperpolarizabilities of 1,3-thiazolium-5-thiolates mesoionic compounds using the hyper-Rayleigh scattering technique, we theoretically investigated the UV-vis absorption spectra and every-order polarizabilities of these mesoionic molecules. Based on the fact that the photophysical and nonlinear properties observed in the experiment can be perfectly replicated, our theoretical calculations explored the essential characteristics of the optical properties of the mesoionic compounds with different electron-donating groups at the level of electronic structures through various wave function analysis methods. The influence of the electron-donating ability of the donor on the optical properties of the molecules and the contribution of the mesoionic ring moiety to their optical nonlinearity are clarified, which have not been reported by any research so far.

Exploring Nature and Predicting Strength of Hydrogen Bonds: A Correlation Analysis Between Atoms-in-Molecules Descriptors, Binding Energies, and Energy Components of Symmetry-Adapted Perturbation Theory.

This work studies the underlying nature of H-bonds (HBs) of different types and strengths and tries to predict binding energies (BEs) based on the properties derived from wave function analysis. A total of 42 HB complexes constructed from 28 neutral and 14 charged monomers were considered. This set was designed to sample a wide range of HB strengths to obtain a complete view about HBs.

Baird's Rule in Substituted Fulvene Derivatives: An Information-Theoretic Study on Triplet-State Aromaticity and Antiaromaticity.

Originated from the cyclic delocalization of electrons resulting in extra stability and instability, aromaticity and antiaromaticity are important chemical concepts whose appreciation and quantification are still much of recent interest in the literature. Employing information-theoretic quantities can provide us with more insights and better understanding about them, as we have previously demonstrated. In this work, we examine the triplet-state aromaticity and antiaromaticity, which are governed by Baird's 4 rule, instead of Hückel's 4 + 2 rule for the singlet state.

A new type of halogen bond involving multivalent astatine: an ab initio study.

Theoretical studies on the dimers formed by CO with the halides of multivalent astatine as a Lewis-acid center are carried out to examine the typical characteristics of supervalent halogen bonds. Calculations at the MP2/aug-cc-pVTZ level reveal that the multiple nucleophilic sites of multivalent halide monomers can promote the formation of various types of halogen bonds, among which the most stable ones are At-halogen bond complexes with multivalent astatine as a Lewis acid center, followed by the π-halogen bond dimers, and the weakest ones are the X-halogen bonds. Compared with multivalent Cl-, Br-, and I-centers, At, as the heaviest halogen, exhibits the highest halogen-bond donating ability.

Using Pauli energy to appraise the quality of approximate semilocal non-interacting kinetic energy density functionals.

It is well-known that the kinetic energy density (KED) functional is the most difficult to approximate in density functional theory (DFT), yet to take full advantage of DFT with its density-based descriptive capability of molecular properties, an accurate account of KED is a must. To have a better idea of how an approximate KED formula behaves and where we should focus in the future development of better approximate KEDs, in this work we propose to employ the Pauli energy to assess their quality. We tested the performance of a total of 22 approximate semilocal noninteracting KED functionals from the literature for 18 neutral atoms and 20 small molecules.

A theoretical investigation on Cu/Ag/Au bonding in XHP⋯MY(X = H, CH, F, CN, NO; M = Cu, Ag, Au; Y = F, Cl, Br, I) complexes.

Intermolecular interaction of XHP···MY (X = H, CH, F, CN, NO; M = Cu, Ag, Au; Y = F, Cl, Br, I) complexes was investigated by means of an method. The molecular interaction energies are in the order Ag < Cu < Au and increased with the decrease of R. Interaction energies are strengthened when electron-donating substituents X connected to XHP, while electron-withdrawing substituents produce the opposite effect.

SCI: a robust and reliable density-based descriptor to determine multiple covalent bond orders.

Very recently [J. Phys. Chem.

Identifying Strong Covalent Interactions with Pauli Energy.

As one of the most widely used chemical concepts whose origin can be traced back to Lewis theory of bonding a century ago, a covalent bond involves sharing one or more pairs of electrons between atoms. A strong covalent interaction (SCI) is such a covalent bond that two or more electron pairs are shared, yielding a double, triple, quadruple, or even higher bond order. Despite its ubiquity and usefulness, a robust and generally applicable approach to accurately identify strong covalent interactions and determine their bond orders is still lacking.

Molecular acidity: An accurate description with information-theoretic approach in density functional reactivity theory.

Molecular acidity is one of the important physiochemical properties of a molecular system, yet its accurate calculation and prediction are still an unresolved problem in the literature. In this work, we propose to make use of the quantities from the information-theoretic (IT) approach in density functional reactivity theory and provide an accurate description of molecular acidity from a completely new perspective. To illustrate our point, five different categories of acidic series, singly and doubly substituted benzoic acids, singly substituted benzenesulfinic acids, benzeneseleninic acids, phenols, and alkyl carboxylic acids, have been thoroughly examined.

A theoretical investigation on doping superalkali for triggering considerable nonlinear optical properties of Si C nanostructure.

In this work, we designed a series of superalkali-doped Si C nanocage M O@Si C (M = Li, Na, K) with donor-acceptor framework. Density functional theory calculations demonstrated that the HOMO-LUMO gap of the complexes conspicuously narrowed with increase of atomic number of the alkali metal, the value decreased from 5.452 eV of pure Si C nanocage to 3.

Electronic forces as descriptors of nucleophilic and electrophilic regioselectivity and stereoselectivity.

One of the main tasks of theoretical chemistry is to rationalize computational results with chemical insights. Key concepts of such nature include nucleophilicity, electrophilicity, regioselectivity, and stereoselectivity. While computational tools are available to predict barrier heights and other reactivity properties with acceptable accuracy, a conceptual framework to appreciate above quantities is still lacking.

Information Functional Theory: Electronic Properties as Functionals of Information for Atoms and Molecules.

How to accurately predict electronic properties of a Columbic system with the electron density obtained from experiments such as X-ray crystallography is still an unresolved problem. The information-theoretic approach recently developed in the framework of density functional reactivity theory is one of the efforts to address the issue. In this work, using 27 atoms and 41 molecules as illustrative examples, we present a study to demonstrate that one is able to satisfactorily describe such electronic properties as the total energy and its components with information-theoretic quantities like Shannon entropy, Fisher information, Ghosh-Berkowitz-Parr entropy, and Onicescu information energy.

Computational Study of Chemical Reactivity Using Information-Theoretic Quantities from Density Functional Reactivity Theory for Electrophilic Aromatic Substitution Reactions.

The electrophilic aromatic substitution for nitration, halogenation, sulfonation, and acylation is a vastly important category of chemical transformation. Its reactivity and regioselectivity is predominantly determined by nucleophilicity of carbon atoms on the aromatic ring, which in return is immensely influenced by the group that is attached to the aromatic ring a priori. In this work, taking advantage of recent developments in quantifying nucleophilicity (electrophilicity) with descriptors from the information-theoretic approach in density functional reactivity theory, we examine the reactivity properties of this reaction system from three perspectives.