Search

The radical cyclization reaction in the aqueous environment by Yorimitsu et al. is revisited using the RISM-SCF-cSED method, a hybrid of quantum chemistry and statistical mechanics theory for molecular liquids. The difference between the barrier height of the forward reaction from the intermediate E -rot, the cyclization step, and that of the backward reaction is crucial to the reaction yield. Considering the effect of hydrogen bonding through the RISM theory, we found that the barrier height for the forward reaction is lower, especially in water. In other words, considering microscopic solvation effects clearly shows the difference between water and DMSO solvents, explaining the remarkable acceleration of the reaction in the aqueous environment. [Display omitted] • The solvent effect on the radical cyclization reaction is analyzed theoretically. • Water solvent promotes the cyclization reaction by lowering its transition state. • Hydrogen bond around C O oxygen atom plays a crucial role on solvent effect of water. • The change in solvation structure along with the C C bond formation is also revealed. [ABSTRACT FROM AUTHOR]

Graphical abstract Nb 2 Si 20 − anion has an irregular Nb 2 -doped endohedral structure, whereas Nb 2 Si 20 neutral adopts C 2h symmetric elongated dodecahedron cage structure. Interestingly, Nb 2 Si 20 −/0 exhibit significant aromaticity. Highlights • Nb 2 Si 20 neutral adopts C 2h symmetric elongated dodecahedron cage structure. • The Nb–Nb interactions in Nb 2 Si 20 −/0 are strong. • Nb 2 Si 20 −/0 exhibit significant aromaticity. Abstract We present a theoretical investigation on the geometric structures and bonding properties of Nb 2 Si 20 −/0 clusters using density functional theory calculations. The results showed that Nb 2 Si 20 − anion has an irregular Nb 2 -doped endohedral structure, whereas Nb 2 Si 20 neutral adopts C 2h symmetric elongated dodecahedron cage structure, which is composed of twelve pentagonal faces. Bond length, Wiberg bond order, constant electronic charge density, and molecular orbital analyses suggest that the Nb–Nb interactions in Nb 2 Si 20 −/0 are strong. Interestingly, Nb 2 Si 20 −/0 exhibit significant 3D aromaticity. [ABSTRACT FROM AUTHOR]

Chemical descriptors using DFT concepts characterize elements reactivity. Hardness and electrophilicity relate to the charge and energy exchanged, determining changes in the length and slope during reaction. Three zones are identified. At low charge exchange (<0.25) the length of the path shortens with constant slope. At higher charge exchange (>0.50) the length increases while its slope rotates. The two regions respectively correspond to frontier molecular orbital and charge-controlled reactions. They relate to the divergence and rotational components of the chemical potential gradient, pointing toward nucleophilic or electrophilic reactions. In between reactions are a mixing both end-member components. [ABSTRACT FROM AUTHOR]

Inferring molecular orientations from vibrational sum frequency generation (SFG) spectra is challenging in polarization combinations that result in low signal intensities, or when the local point group symmetry approximation fails. While combining experiments with density functional theory (DFT) could overcome this problem, the scope of the combined method has yet to be established. Here, we assess its feasibility of determining the distributions of molecular orientations for one monobasic ester, two epoxides and three alcohols at the vapor/fused silica interface. We find that molecular orientations of nonlocal vibrational modes cannot be determined using polarization-resolved SFG measurements alone. [ABSTRACT FROM AUTHOR]

Identification of radiation-induced radicals in relatively simple molecules is a prerequisite for the understanding of reaction pathways of the radiation chemistry of complex systems. Sucrose presents an additional practical interest as a versatile radiation dosimetric system. In this work, we present a periodic density functional theory study aimed to identify the fourth stable radical species in this carbohydrate. The proposed model is a fragment suspended in the lattice by hydrogen bonds with an unpaired electron at the original C5’ carbon of the fructose unit. It requires a double scission of the ring accompanied by substantial chemical and geometric reorganization. [ABSTRACT FROM AUTHOR]

The effects of metal-site substitution into two-dimensional transition metal dichalcogenides (2D-TMDs) to further modify its unique properties remain largely unexplored. This work utilizes first-principles density functional theory (DFT) calculations to quickly explore various concentrations of Ti dopants on 2D-MoS 2 and investigate their effect on structural, electrical, phonon, and optical properties. These effects decrease with concentration until they converge at 2.083 at.% Ti, where the dopants are effectively isolated. These results were then compared with 2.083 at.% V in MoS 2 . Our work reviews the effects of metal-site substitution in 2D-MoS 2 , identifying factors for tailoring the performance of 2D-TMD materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Single-phase samples were prepared by the sol–gel combustion method. • The macroscopic magnetism at room temperature was judged by the magnetization curve and Mössbauer spectrum. • A good thermomagnetic curve was fitted by molecular field theory, and the exact exchange constant was obtained. • The special thermally induced spin behavior of A-site Pr3+ ions are described. Ultrafast spin control plays a pivotal role in condensed matter physics. In this study, we analyzed the macroscopic magnetization of the PrFe 0.1 Cr 0.9 O 3 system by molecular field model fitting. And the whole process of system spin reorientation is accurately calculated in the fitting process. It is found that, unlike the rare-earth perovskites we have previously studied, PrFe 0.1 Cr 0.9 O 3 exhibits spin-reversion properties during the reorientation process. This research will lay a theoretical foundation for precise spin control in the future. [ABSTRACT FROM AUTHOR]

Based on the A λ diagnostic for multireference effects recently proposed [U.R. Fogueri, S. Kozuch, A. Karton, J.M. Martin, Theor. Chem. Acc. 132 (2013) 1], a simple method for improving total atomization energies and reaction energies calculated at the CCSD level of theory is proposed. The method requires a CCSD calculation and two additional density functional theory calculations for the molecule. Two sets containing 139 and 51 molecules are used as training and validation sets, respectively, for total atomization energies. An appreciable decrease in the mean absolute error from 7–10 kcal mol −1 for CCSD to about 2 kcal mol −1 for the present method is observed. The present method provides atomization energies and reaction energies that compare favorably with relatively recent scaled CCSD methods. [ABSTRACT FROM AUTHOR]

Temporal system-mass-density fluctuation analysis was performed on liquid−water molecular-dynamics simulations at ambient pressure and 200 and 300 K, in three increasingly-large systems. A prominent mode in system-density fluctuations was observed at molecular-librational frequencies of ∼600−800 cm −1 (with pronounced temperature dependence). This mode displayed marked system-size dependence, disappearing for larger systems. Persistent system-density fluctuations were clearly evident at 10−11 cm −1 for all systems and temperatures, with lower-amplitude ‘overtones’ evident only in larger systems. It is conjectured that this reflects ∼3 ps timescales observed in earlier studies for dissipation of local-density fluctuations in liquid water in this 200−300 K temperature range. [ABSTRACT FROM AUTHOR]

Highlights: [•] Importance of 1H-2(Phenylazo) imidazole (PaiH) molecule is discussed. [•] Interaction of PaiH with silver nano particles is possibly through theN3 atom. [•] Concentration dependent dark isomerisation (trans-to-cis) is suggested. [•] DFT calculations are in good agreement with experimental results. [ABSTRACT FROM AUTHOR]

Abstract: Here we develop a molecular theory attempting to answer the long-standing questions regarding the decoupling of dielectric friction from dipolar solute rotation in various liquid systems: ionic liquids, electrolyte solutions and polar solvents. Using both experimental and model solvent structure factors, we show insignificant dielectric friction and provide microscopic explanation for the experimentally observed domination of hydrodynamics in solute rotation in these media. Our analyses lead to a macro–micro relation indicating a quasi-universality in solute rotation for a wide variety of solute–solvent combinations. We demonstrate that both the quasi-universality and the domination of hydrodynamics originate from packing at liquid-like density. [Copyright &y& Elsevier]

Abstract: A semi-molecular theory has been employed to predict temperature dependent Stokes shift dynamics of a dipolar probe in sodium 2,5,8,11-tetraoxatridecan-13-oate ([Na][TOTO]), and compared with imidazolium ionic liquids (ILs). Predicted dynamic Stokes shift for [Na][TOTO]is ∼60–70% of that calculated for imidazolium ILs. The calculated biphasic dynamics is, however, extremely slow because of large viscosity, average solvation time (〈τ ss〉) being in ∼1s–10ns range at 254⩽ T/(K)⩽344. This is much slower than those in imidazolium ILs (0.1⩽〈τ ss〉/ns⩽6 at 278⩽ T/(K)⩽338). Predicted temperature dependence of shift is very weak and suggests near-Arrhenius behavior for the dynamics. [Copyright &y& Elsevier]

Abstract: A molecular theory is employed to predict the Stokes’ shift dynamics for a dipolar solute, C153, in six different alkylimidazolium ionic liquids (ILs) containing a fixed anion, tetra(hexafluoroisopropoxy)aluminate. Calculated shifts in these ILs at ∼343K range ∼2300–3700cm−1, and a dominating contribution (∼75–85%) arises from the solute-IL dipole–dipole interaction. Inclusion of solvent-libration predicts ∼50% ultrafast component in the total dynamics. Although the predicted dynamics is faster than in other ILs, calculated shifts follow the same linear correlation with ion size-ratio. Furthermore, model calculations explore the solute-IL size-ratio dependence of the interaction contributions to the shift, and investigates the relative importance of solvent rotational and translational modes for IL dynamics. [Copyright &y& Elsevier]

Abstract: Fluorescence dynamics of a polar solute probe in molten (CH3CONH2 +Ca(NO3)2·4.37H2O) mixtures have been measured in order to probe the solute–medium interactions in such complex systems. Steady state and time-resolved measurements bear no signatures of mega-value of the static dielectric constant, strong heterogeneity and extremely slow relaxation times reported in dielectric relaxation experiments for these molten mixtures. Subsequent applications of a semi-molecular theory reveal both the solute–medium dipole–dipole and ion–dipole interactions contribute significantly to the measured Stokes’ shifts. Calculated average solvation times in the underdamped and overdamped limits of frictional solvent response agree semi-quantitatively with those from time-resolved measurements. [ABSTRACT FROM AUTHOR]

Abstract: Epstein [P.S. Epstein, Phys. Rev. 23 (1924) 710] provided the benchmark analysis for a series of expressions describing the drag force exerted on small moving particles by an ideal gas media. His expression for elastic collisions shows that the drag force increases according to the function 1+4s/9, in which s is the fraction of molecules diffusively reflected. For inelastic collisions in which the particles are thermally conducting and non-conducting, the drag force increases as 1+πs/8 and 1+9πs/64, respectively. Analysis using configuration-specific kinetic molecular theory reproduces Epstein’s expression for the drag force where s =0, but predicts that the drag force decreases according to the function 1-s/6. This work also includes an expression for s derived from Massalimov’s [I.A. Massalimov, Chem. Sust. Dev. 10 (2002) 119] equation for the probability of phonon energy transmission. [Copyright &y& Elsevier]

[Display omitted] • The 3D Reference Interaction Site Model is used to explore liquid oleyl alcohol. • The 3D-RISM simulations produced the liquid oleyl alcohol structure qualitatively similar to the MD simulation. • The united atom TRAPPE force field is used for bulk susceptibility calculation of the liquid. • The molecular partitioning in alcohol/water media is calculated with RMSD of 0.48 unit. • A new QSAR model is presented for the partition function calculation. The 3D-RISM-KH molecular solvation theory is applied to liquid long chain unsaturated oleyl alcohol to explore the structure of the liquid and to calculate alcohol/water partition coefficients. The united atom TraPPE force field parameters resulted in comparable structural information between RISM and MD simulations. The RISM theory and the MD simulation point to a relatively ordered liquid structure of oleyl alcohol. The molecular partition coefficients were computed with a root mean square deviation of 0.48 unit via a predictive quantitative structure activity relationship. [ABSTRACT FROM AUTHOR]

The effects brought about by several substitutions on the acidity of 16 phenol derivatives have been studied by using atoms in molecules (AIM) theory on electron charge densities obtained at the B3LYP/6-31++G**//B3LYP/6-31G** level. The obtained results allow us to conclude that when the substituent induces an increase in the acidity of the compound. Increases are also found in the strength of the OH and CO bonds. Atomic populations and delocalization indexes can also be related to the acidic character, although these properties as calculated by AIM theory cannot be related to predictions provided by the resonance model. [Copyright &y& Elsevier]

The implementation and the validation of a simple, self-consistent method to correct the self-interaction error in density functional theory approaches is presented. This model is based on an average density self-interaction correction. The main advantage of the method rests on its simplicity and favorable scaling with the size of the system. We have tested this method on one of the classical pathological problem for density functional theory: the direct estimation of the ionization potential from orbital eigenvalues. The proposed method provides good values for delocalized molecular systems, while large deviations, are obtained for atomic or strongly localized molecular systems. [Copyright &y& Elsevier]

The van der Waals complex between the Cl(2P) atom and the HCl molecule was carefully investigated. Using high-level ab initio molecular orbital theory with extended basis sets, we analyse the effects of level of calculation, spin projection, basis set superposition error (BSSE), spin–orbit coupling, and harmonic zero-point energy (ZPE) on the energy changes. The non-collinear approach (12A′ ground state) shows a deeper well at 0 K, 401 cm−1, than the collinear approach (2Π ground state), 329 cm−1. It is concluded that these results represent the balance of a complicated interplay of many factors, which are affected by uncertainties in the theoretical calculations. [Copyright &y& Elsevier]

We report Monte Carlo simulations of chemical potentials on short ranging primitive models (PM) of water due to Nezbeda and co-workers. Since Widom’s test particle method fails for network forming PM water, we simulate chemical potentials by gradual particle insertion. From chemical potential versus packing fraction isotherms, we estimate densities of coexisting phases by means of a Maxwell equal-area rule. Site–site correlation functions, cluster size distributions, and mean square displacements of coexisting phases are analysed. The presented chemical potentials and coexistence properties should be considered as important reference data for PM based molecular theories of associating fluids. [Copyright &y& Elsevier]

Atomic valence in molecular systems is described as a partitioning of the hole distribution, the complementary part of the particle distribution. In this scheme, valence splits into three contributions, related to electron spin density, nonuniform occupancy of orbitals (nonpairing terms) and exchange density (pairing terms), respectively, and whose importance depends on the nature of the state of the system. Calculations carried out for correlated CI and Hartree–Fock state functions in both Mulliken and topological AIM type partitionings as well as theoretical results show the suitability of this formulation for describing valence concepts. [Copyright &y& Elsevier]

A general formalism is developed for the theory of electronic current through a molecule attached to macroscopic electrodes in a given bias. The current is calculated in a non-perturbative many-body formalism. We obtain an intuitively appealing formula. We identify two distinct limits: the Kubo linear response formula valid in the small bias regime and the Landauer formula valid for non-interacting electrons. Finally, we develop a new correlation function formula, which is more amenable to numerical computations and discuss the application of absorbing potentials in the electrodes as a possible means of calculation. [Copyright &y& Elsevier]

A novel theory of vibronic intensity borrowing by large-amplitude vibrations was developed in a form to modify the conventional Herzberg–Teller theory. The ingredients are: (1) Crude Born–Oppenheimer wavefuntions (CBO Wf’s) at more-than-one (2×2×3=12) conformations were used as building blocks of the adiabatic BO Wf. (2) The latter was made to belong to the molecular symmetry group (G12) by Fourier-series expansion terminated at the low (ninth) order. (3) The non-Born–Oppenheimer effect was shown to be less significant. The experimental observation of the subtitle was successfully interpreted with this formalism, endorsing the previous assertion by Walker et al. [J. Chem. Phys. 102 (1995) 8718]. [Copyright &y& Elsevier]

Structural properties of energetically low-lying stationary points of the MgSiO3 molecular system have been investigated by theoretical density functional techniques. A large number of singlet and triplet structures representing local minima of the neutral MgSiO3 molecule are completely characterised. The energetically lowest of these minima is a singlet state of planar kite-shaped C2v symmetry. The system equally possesses a variety of stable charged species of which the respectively lowest in energy is presented. We report energies, equilibrium geometric parameters, selected harmonic vibrational wave numbers along with corresponding absorption coefficients. Stability and geometric aspects are compared to the molecules Si2O3 and Mg2O3, as well as to the isoelectronic Al2O3 molecular system. [Copyright &y& Elsevier]

• [P 1111 ][Gly] and [P 4444 ][Gly] were analyzed for CO 2 absorption capacity. • Reaction mechanism for CO 2 absorption was unveiled using DFT. • MD simulation used to understand the physical properties of ionic liquids. • Effect of water on ionic strength was also evaluated. Carbon dioxide is a well-known greenhouse gas that cause global warming. CO 2 capture and sequestration strategy is known promising strategy to reduce the level of CO 2 in the atmosphere. Thus, the usage of Amino Acid Ionic Liquids have gained attention for reversible CO 2 capture. Herein, we use DFT to report the effect of CO 2 chemisorption on tetramethylphosphonium glycinate and tetrabutylphosphonium glycinate ILs. Finally, Molecular Dynamics (MD) simulations were carried out to study the physicochemical properties of ILs in pure form and in the presence of explicit water. Overall, our study confirms the usage of studied ILs to efficiently capture CO 2. [ABSTRACT FROM AUTHOR]