Surface tension is one of the most important properties of liquid. A new theory is proposed and applied to the phenomena related to the surface tension of pure liquid compounds and strong electrolyte solutions. We first found that the phase transitions of pure liquid compounds from bulk to surface are exothermic and transition heats of 38 liquid compounds are determined quantitatively. This theory also describes successfully the variations of the surface tensions with the concentrations of solutes in strong electrolyte solutions. As a byproduct, minimum thicknesses of the surface layers of these solutions are deduced.Download high-res image (48KB)Download full-size image

•An unexplored epoxy/low-molar-mass-mercaptan curing system was used to prepare PDLC films.•The polymer morphology in this system could be regulated from polymer beads to porous polymer matrix.•The relationship between the electro-optical properties and the polymer structures was established.•E-O properties can be optimized by turning the polymer structures although decrease the LCs content.Morphologies of polymer networks are playing a key role in affecting the electro-optical (E-O) properties of a polymer dispersed liquid crystals (PDLCs) material. In this paper, the relationships between the polymer morphologies and the E-O properties of PDLCs are investigated in an unexplored thermally curing system based on epoxy/low-molar-mass-mercaptan. The polymer morphologies in this curing system can be regulated from polymer beads to porous polymer matrix by varying the liquid crystals (LCs) contents, chemical structures of epoxy monomers, and functionality of thiol hardeners. Interestingly, great improvements of E-O properties occur as the polymer structures change from polymer beads to porous frameworks, even though with an abnormal low LCs contents. Eventually, the mechanism for the formation of different polymer structures are illustrated and the relationships between the E-O properties and polymer structures are established. This work provides new insights in morphology control and optimizing the E-O properties in thermally cured PDLCs films.Download high-res image (268KB)Download full-size image

Predicting the reactivity of nucleophilic reaction at different sites has important theoretical and practical significance. Many prediction methods solely based on the electronic structure of reactants have been proposed. In this paper, detailed comparative analyses on the reliability of 14 methods are carried out and three series of molecules, carbonyl compounds, aromatic hydrocarbons and pyridine derivatives are exploited as test systems. It is found that the methods reflecting local electronic softness, such as condensed dual descriptor, have satisfactory prediction ability; while the ones reflecting electrostatic effect, such as atomic charge analysis and electrostatic potential analysis, have evidently worse overall performance. For all systems of interest, condensed dual descriptor and Hirshfeld charge display the most robust predictive capacity.

Bond order is an important concept for understanding the nature of a chemical bond. In this work, we propose a novel definition of bond order, called the Laplacian bond order (LBO), which is defined as a scaled integral of negative parts of the Laplacian of electron density in fuzzy overlap space. Many remarkable features of LBO are exemplified by numerous structurally diverse molecules. It is shown that LBO has a direct correlation with the bond polarity, the bond dissociation energy, and the bond vibrational frequency. The dissociation behavior of LBO of the N–N bond in N2 has been studied. Effects of the basis sets, theoretic methods, and geometrical conformations on LBO have also been investigated. Through comparisons, we discussed in details similarities and discrepancies among LBO, Mayer bond order, natural localized molecular orbital bond order, fuzzy overlap population, and electron density at bond critical points.

Quantitative analysis of molecular surface is a valuable technique for analyzing non-covalent interaction, studying molecular recognition mode, predicting reactive site and reactivity. An efficient way to realize the analysis was first proposed by Bulat et al. (J. Mol. Model., 16, 1679), in which Marching Tetrahedra (MT) approach commonly used in computer graphics is employed to generate vertices on molecular surface. However, it has been found that the computations of the electrostatic potential in the MT vertices are very expensive and some artificial surface extremes will be presented due to the uneven distribution of MT vertices. In this article, we propose a simple and reliable method to eliminate these unreasonably distributed surface vertices generated in the original MT. This treatment can save more than 60% of total analysis time of electrostatic potential, yet the loss in accuracy is almost negligible. The artificial surface extremes are also largely avoided as a byproduct of this algorithm. In addition, the bisection iteration procedure has been exploited to improve accuracy of linear interpolation in MT. The most appropriate grid spacing for surface analysis has also been investigated. 0.25 and 0.20 bohr are recommended to be used for surface analysis of electrostatic potential and average local ionization energy, respectively.Graphical abstractWe presented a simple and efficient method to eliminate redundant vertices produced by standard Marching Tetrahedra approach. More than 60% of time cost in quantitative analysis of molecular surface of electrostatic potential can be saved without evident deterioration of accuracy of the results.Highlights► A new surface refinement method is applied to quantitative molecular surface analysis. ► More than 60% of time cost in surface analysis can be saved by eliminating unreasonably distributed vertices. ► Bisection algorithm improves interpolation accuracy in Marching Tetrahedra significantly. ► Optimal grid spacing for surface analysis was explored.

A few open-shell molecules are taken as examples in order to examine the performance of the open-shell perturbation theory for electron correlation (J Chem Theory Comput, 2009, 5: 931–936). The convergence of the perturbation series is shown to be stable for the doublet state of NH2 at both the equilibrium and stretched geometries. The equilibrium bond lengths, and harmonic and anharmonic vibrational frequencies are calculated for NO(X2Π), OH(X2Π), CH(X2Π) and NH(X2Σ−) with different second-order perturbation theories at the cc-pVDZ, cc-pVTZ and cc-pVQZ levels. The ground state energies of BeF(X2Σ+), MgH(X2Σ+) and the HCCl triplet state have also been computed with various perturbation theories and compared with configuration interaction with single and double excitations (CISD) and CISD + Davidson correction. The energy difference between the formaldehyde (H2CO+) and hydroxymethylene (HCOH+) radical cations has been computed. Our perturbation theory predicts correctly that H2CO+ is more stable than HCOH+. However, calculations using UMP2, CASPT2, the Z-averaged perturbation theory and restricted Møller-Plesset theory fail even to produce the correct sign of the energy difference.