Structures and Electronic Properties of Cu_N (N≤13) Clusters

A systematic study on the structures and electronic properties of copper clusters has been performed using the density functional theory. In the calculation, there are many isomers near the ground state for small copper clusters. Our results show that the three-dimensional isomers of copper clusters start from Cu7 cluster and then show a tendency to form more compact structures. The results of the formation energy and the second derivative of binding energy with duster size show that besides N = 8, N =11 is also a magic number. Furthermore, it is the first time to find that the ground state of 11-atom clusters is a biplanar structure as same as the 13-atom cluster. The clear odd-even alternation as cluster size for the formation energy indicates the stability of electronic close shell existed in the range studied.

A Group Contribution Method for the Correlation of Static Dielectric Constant of Ionic Liquids

Static dielectric constant is a key parameter to estimate the electro-viscous effect which plays important roles in the flow and convective heat transfer of fluids with ions in microfluidic devices such as micro reactors and heat exchangers.A group contribution method based on 27 groups is developed for the correlation of static dielectric constant of ionic liquids in this paper.The ionic liquids considered include imidazolium,pyridinium,pyrrolidinium,alkylammonium,alkylsulfonium,morpholinium and piperidinium cations and various anions.The data collected cover the temperature ranges of 278.15-343.15 K and static dielectric constant ranges of 9.4-85.6.The results of the method show a satisfactory agreement with the literature data with an average absolute relative deviation of 7.41%,which is generally of the same order of the experimental data accuracy.The method proposed in this paper provides a simple but reliable approach for the prediction of static dielectric constant of ionic liquids at different temperatures.

Tuning optical properties of MOF-based thin films by changing the ligands of MOFs

The preparation and development of novel optical thin films are of great importance to functional optical and opto-electric components requiring a low refractive index.In this study, a typical metal-organic framework（MOF）, MIL-101（Cr）, is selected as the research model. The corresponding MOF nanoparticles are prepared by a hydrothermal method and the optical thin films are successfully prepared by spincoating. The optical properties of the corresponding MOF thin films are controlled by changing the type of functional groups on the benzene ring of the ligand（terephthalic acid） on MOFs.The functional groups are hydrogen atoms（H）,electron donating groups（-NH_2,-OH） and electron withdrawing groups（-NO_2,-（NO_2）_2 or F_4）, respectively. It is found that the effective refractive index（n_（eff）） of MOF thin films decreases along with the increasing voids among MOF nanoparticles. In addition, the extinction coefficient（k） increases with the addition of electron donating groups, and decreases with the addition of electron withdrawing groups. Among the MOFs used in this study, the n_eff of NO_2-MIL-101（Cr） containing electron withdrawing groups is as low as ~1.2, and value of k is particularly low, which suggests its potential application in antireflective devices. In addition, the intrinsic refractive index（n_（dease）） of the dense MOF materials evaluated according to their porosity increases with the number of the functional groups, and the n_（dense） of the two nitro-substituted MOFs is greater than that of the single nitro-substituted one, and the latter is bigger than that of hydroxyl-substituted one, which is close to that of amino-functionalized one. The diversity of ligands in MOFs makes them a promising new generation of optical materials.

Hydrophobicity and carbonation treatment of earthen monuments in humid weather condition

Water stability of soil is crucial to the durability of earthen monuments,especially those located in the humid weather condition.This paper discusses the selection reason of materials(tung oil and quicklime) for earthen monument treatment,and then validates the applicability of these materials with tests of soil-water characteristic curve(SWCC),aggregate stability test(AST) and scanning electron microscope(SEM).The soil tested was sampled from Da Bao'en temple in Nanjing,Jiangsu province,China.The test results indicate that the carbonation reaction of quicklime offers a favorable environment for the formation of tung oil film.Meanwhile,the regulatory function of tung oil restricts the crystallinity of calcium carbonate(CaCO3) and forms fine crystals.Soil treated with both of tung oil and quicklime has good water repellency and aggregate stability without obvious changing in aesthetic appearance.Hydrophobicity and carbonation treatment can be applied prospectively in the conservation of earthen monument located in humid weather condition.

The effect of end-capping groups in A-D-A type non-fullerene acceptors on device performance of organic solar cells

A series of novel wide bandgap small molecules(IFT-ECA, IFT-M, IFT-TH and IFT-IC) based on the A-D-A structure with indenofluorene core, thiophene bridge, and different electron-deficient end-capping groups, were synthesized and used as non-fullerene acceptors in organic solar cells. The influences of end-capping groups on the device performance were studied.The four materials exhibited different physical and chemical properties due to the variation of end-capping groups, which further affect the exciton dissociation, charge transport, morphology of the bulk-heterojunction films and device performance. Among them, IFT-IC-based device delivered the best power conversion efficiency of 7.16% due to proper nano-scale phase separation morphology and high electron mobility, while the devices based on the other acceptors achieved lower device performance(4.14% for IFT-TH, <1% for IFT-ECA and IFT-M). Our results indicate the importance of choosing suitable electron-withdrawing groups to construct high-performance non-fullerene acceptors based on A-D-A motif.