Evaluating interaction energy versus electron density relationships to estimate inter and intramolecular H-bonding.

We investigate the computational effects on the relationships between interaction energy (ΔE) and electron density (ρ), at the critical point obtained from 19 intermolecular H-bonded dimers, to estimate inter and intramolecular interactions of larger H-bonded systems. Our analysis examines basis set superposition error (BSSE) effects, dispersion energy corrections, and the exchange-correlation energy model on the ΔE vs. ρ linear regressions.

A theoretical study of the photochemistry of 1,3-cyclopentadiene and its cyano derivatives bound to a water dimer: Assessing reactivity of ionized clusters and possible photoproducts.

We theoretically investigate the photoionization scenarios of molecular complexes involving cyclopentadiene and cyanocyclopentadiene bound to water dimers. Using electronic structure calculations within density-functional theory (DFT) and time dependent DFT (TD-DFT), we explore the potential photochemical pathways following ionization, and determine the charge transfer excitations related to the possible subsequent reactions. Our findings suggest that the investigated photochemical pathways of the hydrated complexes take place in two well-defined ultraviolet regions: (i) 8.

Influence of Solvents and Halogenation on ESIPT of Benzimidazole Derivatives for Designing Turn-on Fluorescence Probes.

This work reports a theoretical investigation of the solvent polarity as well as the halogenation of benzimidazole derivatives during excited state intramolecular proton transfer (ESIPT). It details how the environment and halogen substitution may contribute to the efficiency of ESIPT upon keto-enol tautomerism and exploits this effect to design fluorescence sensing. For this purpose, we first examine the conformational equilibrium of benzimidazole derivatives containing different halogen atoms, which results in intramolecular proton transfer, using density-functional theory (DFT) combined with the polarizable continuum model (PCM).

Predicting pressure-dependent rate constants for the furan + OH reactions and their impact under tropospheric conditions.

In this work, we have evaluated the influence of temperature and pressure on the mechanism of furan oxidation by the OH radical. The stationary points on the potential energy surface were described at the M06-2X/aug-cc-pVTZ level of theory. In the kinetic treatment at the high-pressure limit (HPL), we have combined the multistructural canonical variational theory with multidimensional small-curvature tunneling corrections and long-range transition state theory.

Regioselectivity in the Nitration of Eugenol Is Independent of Inorganic Reagents: An Experimental and Theoretical Investigation with Synthetic and Mechanistic Implications.

In this study, we reinvestigated the straightforward nitration of eugenol using traditional reagents and bismuth nitrate. NMR analysis of the obtained products revealed that the regioselectivity of eugenol nitration was independent of the inorganic nitrating reagent used, consistently resulting in the formation of 6-nitroeugenol. This contradicts previous literature reports because the elusive synthesis of 5-nitroeugenol using Bi(NO)·5HO was not achievable through straightforward methods; instead, this isomer could only be prepared via the well-established three-step synthesis.

Photoabsorption of Microhydrated Naphthalene and Its Cyano-Substituted Derivatives: Probing Prereactive Models for Photodissociation in Molecular Clouds.

We investigate the photoionization pathways of naphthalene, 1-cyanonaphthalene, and 2-cyanonaphthalene upon complexation with the water dimer, aiming to understand the photodissociation process under conditions of the interstellar medium (ISM). We analyze the intermolecular bonding pattern, equilibrium rotational properties, energy complexation, far-IR spectra, and ionic trends of the possible photoproducts using dispersion-corrected density functional theory (DFT-D) and time-dependent DFT (TD-DFT). For the different configurations, we evaluate the possible charge-transfer (CT) excitations near the photoionization limit.

A Theoretical Assessment of Spin and Charge States in Binuclear Cobalt-Ruthenium Complexes: Implications for a Creutz-Taube Model Ion Separated by a C-Derivative Bridging Ligand.

We investigate the spin-state energetics and the role of ionic charges in the electronic configuration of binuclear complexes of the form [(NH)Co(py)-X-(py)Ru(NH)]. In these compounds with = 4-6, py = pyridine, and X = C≡C and C, the Co-Ru distance varies from ∼1.4 to ∼2.

Optical properties of organosilicon compounds containing sigma-electron delocalization by quasiparticle self-consistent GW calculations.

We investigate theoretically the electronic and optical absorption properties of two sub-classes of oligosilanes: (i) Si(CH), Si(CH), and Si(CH) that contain Si dot, ring and cage, respectively, and exhibit typical SiC and SiSi bonds; and (ii) persilastaffanes SiH(CH) and SiH(CH), which contain extended delocalized σ-electrons in SiSi bonds over three-dimensional Si frameworks. Our modeling is performed within the GW approach up to the partially self-consistent GW approximation, which is more adequate for reliably predicting the optical band gaps of materials. We examine how the optical properties of these organosilicon compounds depend on their size, geometric features, and Si/C composition.

Modeling the Field Emission Enhancement Factor for Capped Carbon Nanotubes Using the Induced Electron Density.

In many field electron emission experiments on single-walled carbon nanotubes (SWCNTs), the SWCNT stands on one of two well-separated parallel plane plates, with a macroscopic field  applied between them. For any given location "L" on the SWCNT surface, a field enhancement factor (FEF) is defined as /, where is a local field defined at "L". The best emission measurements from small-radii capped SWCNTs exhibit characteristic FEFs that are constant (i.

Close Relationships between NMR J-Coupling Alternation (JCA) and Molecular Properties of Carbon Chains.

We propose a J-coupling alternation (JCA) value that is demonstrated to be a suitable parameter to evaluate the nuclear magnetic resonance (NMR) indirect spin-spin coupling constants (SSCCs) as a function of molecular properties of chains by increasing their length. As an application, we report a theoretical study of the SSCCs for the interactions between neighbor nuclei in increasingly patterned carbon chains within density functional theory. First, we examine the J-coupling constants between H and C nuclei ( J) considering the separation distance, as well as between two adjacent C nuclei ( J) considering their relative positions in polyynes and cumulenes.

Self-Healing in Carbon Nitride Evidenced As Material Inflation and Superlubric Behavior.

All known materials wear under extended mechanical contacting. Superlubricity may present solutions, but is an expressed mystery in C-based materials. We report negative wear of carbon nitride films; a wear-less condition with mechanically induced material inflation at the nanoscale and friction coefficient approaching ultralow values (0.

Probing Lewis Acid-Base Interactions with Born-Oppenheimer Molecular Dynamics: The Electronic Absorption Spectrum of p-Nitroaniline in Supercritical CO2.

The structure and dynamics of p-nitroaniline (PNA) in supercritical CO2 (scCO2) at T = 315 K and ρ = 0.81 g cm(-3) are investigated by carrying out Born-Oppenheimer molecular dynamics, and the electronic absorption spectrum in scCO2 is determined by time dependent density functional theory. The structure of the PNA-scCO2 solution illustrates the role played by Lewis acid-base (LA-LB) interactions.

A first principles approach to the electronic properties of liquid and supercritical CO2.

The electronic absorption spectra of liquid and supercritical CO2 (scCO2) are investigated by coupling a many-body energy decomposition scheme to configurations generated by Born-Oppenheimer molecular dynamics. A Frenkel exciton Hamiltonian formalism was adopted and the excitation energies were calculated with time dependent density functional theory. A red-shift of ∼ 0.

Including thermal disorder of hydrogen bonding to describe the vibrational circular dichroism spectrum of zwitterionic L-alanine in water.

The vibrational circular dichroism (VCD) spectrum of l-alanine amino acid in aqueous solution in ambient conditions has been studied. The emphasis has been placed on the inclusion of the thermal disorder of the solute-solvent hydrogen bonds that characterize the aqueous solution condition. A combined and sequential use of molecular mechanics and quantum mechanics was adopted.

Origin of the Red Shift for the Lowest Singlet π → π* Charge-Transfer Absorption of p-Nitroaniline in Supercritical CO2.

The origin of the unusual solvatochromic shift of p-nitroaniline (PNA) in supercritical carbon dioxide (SCCO2) is theoretically investigated on the basis of experimental data. Ab initio quantum chemistry calculations have been employed to unveil the interaction of CO2 with this archetypical molecule. It is demonstrated that the nitro group of PNA works as an electron-donating site binding to the electron-deficient carbon atom of CO2, most probably via a Lewis acid-base interaction.

Unusual electronic properties and transmission in hexagonal SiB monolayers.

After the success of graphene, several two-dimensional (2D) layers have been proposed and investigated both theoretically and experimentally in order to evaluate their structural stability and possible applications of these unusual materials in electronics. Except for graphene, only silicon and germanium were predicted to form semi-metallic honeycomb monolayers, while most of the binary graphene-like compounds are all semiconductors. These predictions have been corroborated for several 2D structures experimentally synthesized.

Exploring hydrogenation and fluorination in curved 2D carbon systems: a density functional theory study on corannulene.

Corannulene has been a useful prototype for studying C-based nanostructures as well as surface chemistry and reactivity of sp(2)-hybridized carbon-based materials. We have investigated fluorination and hydrogenation of corannulene carrying out density functional theory calculations. In general, the fluorination is energetically more favorable than hydrogenation of corannulene.

Optical response of liquid acetonitrile at ambient conditions: the dynamical dielectric behavior from ab initio calculations.

We probe the linear optical properties of the neat liquid acetonitrile (CH(3)CN) at ambient conditions using ab initio density functional theory. Uncorrelated structures extracted from Monte Carlo simulation are employed to efficiently calculate average electronic properties. It becomes evident that condensation leads to a conduction band with a large degree of dispersion, which is consistent with the description of dipolar liquids.

Note on the free energy of transfer of fullerene C60 simulated by using classical potentials.

Diverse atomistic parameters of C60 have been developed and utilized to simulate fullerene solutions in biological environments. However, no thermodynamic assessment and validation of these parameters have been so far realized. Here, we employ extensive molecular dynamics simulations with the thermodynamic integration method in the isothermal-isobaric ensemble to investigate the transfer of a single fullerene C60 between different solvent environments using different potential models.

Effects of hydroxyl group distribution on the reactivity, stability and optical properties of fullerenols.

We investigate the impact of hydroxyl groups on the properties of C(60)(OH)(n) systems, with n = 1, 2, 3, 4, 8, 10, 16, 18, 24, 32 and 36 by means of first-principles density functional theory calculations. A detailed analysis from the local density of states has shown that adsorbed OH groups can induce dangling bonds in specific carbon atoms around the adsorption site. This increases the tendency to form polyhydroxylated fullerenes (fullerenols).

Lewis acid-base interactions in weakly bound formaldehyde complexes with CO2, HCN, and FCN: considerations on the cooperative H-bonding effects.

Ab initio quantum chemistry calculations reveal that HCN and mainly FCN can form Lewis acid-base complexes with formaldehyde associated with cooperative H bonds, as first noticed by Wallen et al. (Blatchford, M. A.

Structure and UV-vis spectrum of C(60) fullerene in ethanol: a sequential molecular dynamics/quantum mechanics study.

A molecular dynamics simulation combined with semiempirical quantum mechanics calculations has been performed to investigate the structure, dynamical, and electronic properties of pure C60 in liquid ethanol. The behavior of the fullerene alcoholic solution was obtained by using the NPT ensemble under ambient conditions, including one C60 fullerene immersed in 1000 ethanol molecules. Our analyzed center-of-mass pairwise radial distribution function indicated that, on average, there are 32, 72, 132, and 187 ethanol molecules around, respectively, the first, second, third, and fourth solvation shells of the C60 molecule.

Band gap and density of states of the hydrated C60 fullerene system at finite temperature.

We examine the electronic properties of the hydrated C60 fullerene under ambient conditions using a sequential Monte Carlo/density functional theory scheme. In this procedure, the average electronic properties of the first hydration shell of C60 equilibrate for ca. 40 uncorrelated configurations of the fullerene aqueous solution.