Qn Zhang

The influence of water on dielectric property in cocrystal compound of [orotic acid][melamine]·H2O

An organic cocrystal compound consisting of melamine, orotic acid and water molecules was synthesized under hydrothermal conditions. Investigation of its temperature- and frequency-dependent dielectric behaviors reveals that the fluctuation of hydrogen atoms of water molecules between the layers plays a key role in its dielectric anomaly.

An above-room-temperature switchable molecular dielectric with a large dielectric change between high and low dielectric states

Dielectric anisotropy of anilinium perchlorate is investigated at various temperatures. Crystal structures at different temperatures reveal that significant dielectric change between low and high dielectric states is closely related to the disorder of the anilinium cation and perchlorate anion at high dielectric state; meanwhile, the conductivity after phase transition also contributes a lot to the high dielectric state.

Studies on cluster-surf ace analogy: ab initio calculations for the CO/Ni chemisorption system

After exploring the underlying physics of the cluster-surface analogy, we introduce the concept of “metallic atom”. Case studies of the Ni-CO cluster as a model of CO/Ni chemisorption are carried out with UHF/STO-3G of the so-called atomic ζa and metallic ζm, where ζa is a basis function optimized from the ground state of a Ni atom, while ζm is a modifier of ζa based the free-electron theory in solid state physics. The calculation results of ζa and ζm are elucidated in the light of more rigorous cluster calculations in the literature.

Electronic structures of osmium dinitrides and dinitrogen molecule activation by the osmium atom

Density functional theory and ab initio electron-correlation methods have been used to study structures, stabilities, and bonding properties of osmium dinitrides, and possible mechanisms for the direct insertion of osmium into the strong dinitrogen triple bond. At B3LYP, CCSD//B3LYP. and QCISD levels, the end-on linear OsNN species in the 3Σ− state with a δ2 electron configuration is found to be the most stable isomer, whereas CCSD(T)//B3LYP, QCISD(T)//QCISD, and CASSCF(12,11)//QCISD calculations result in an inserted NOsN species in the singlet 1A1 state as the lowest energy state. The direct insertion reactions of osmium into the dinitrogen triple bond, involved in specific low-lying electronic states of the osmium dinitrides, are exothermic, and the activation energies are in the range 3.9–21.8 kcal mol−1 Natural population analyses show that the unoccupied 6p orbital in the osmium ground state configuration may play an important role in the dinitrogen molecule activation by osmium.

SPC cluster modeling of metal oxides: ways of determining the values of point charges in the embedded cluster model

Several criteria for determining self-consistently the magnitude of point charges employed in the embedded cluster modeling of metal oxides have been proposed and investigated. Merits and demerits of these criteria have been compared.Ab initio study has been performed to show the influence of the values of point charges chosen on the calculated electronic properties of the embedded MgO cluster. The calculation results demonstrate that the electronic properties of the embedded cluster are of great dependence on the magnitude of the embedding point charges; that the employment of the nominal charges, ±2.0, would cause overestimation of the crystal potential even in the case of the so-called purely ionic oxide. MgO; and that certain requirements for the consistence between the embedded cluster and the embedding point charges should be reached. It is further found that errors for the calculated properties of the embedded cluster still exist with respect to those of bulk solid even in the case that self-consistence in terms of charge, dipole moment, or electrostatic potential was met between the cut-out cluster and the embedding point charges. As far as spherical expansion is performed upon the embedding point charges, which furnishes the embedding point charges with a continuous distribution of charge density, a global agreement is reached between the calculated properties of the embedded cluster model and those of the bulk solid.