A theoretical study on the magneto-structural correlation in binuclear Cu (Ⅱ) complexes bridged by the imidazolate anion has been performed using the broken-symmetry approach with the framework of density functional theory (DFT). The calculated results show that the variational trends of the magnetic coupling constant J with geometrical parameters are different for two models. The magnetic coupling constant J mainly depends on the Cu-N-C (im) bond angle ф and is insensitive to the variation of the Cu-N (im) distance and the dihedral angle a between the bridged imidazolate ring and copper coordination planes. The dependence of J on the angle ф in the two models shows that the J values are equal when the Cu-N-C(im) angle f 128.

During hot-dipping in molten Zn-55Al, the forming of "floating" dross is closely related with the interaction between the Al and the Fe atoms. Utilizing the thita-thita X-ray diffraction and the Percus-Yevick hard sphere model, this paper investigates the structure of molten Al3Fe that is an approximant of partial melt in practical Zn-55Al alloy melt. It is found that in the melt there exist clusters that resemble the structure of intermetallic compound Al3Fe. The strong interaction between Al and Fe atoms is also indicated by the deficiency of the coordination number from 12 and the shrinkage of averaged atomic diameter. Based on such information, it is speculated that in the molten Zn-55Al, with the accumulation of Fe, Al3Fe-like clusters form with priority, then grow into dross. On the other hand, after deflating of the effective hard sphere diameter of pure Al atom and enlarging that of the pure Fe atom, the modified model can achieve reasonable fit to the experimental structure factor. Hard sphere modeling also gave a good estimation of the mass density 3.65g/cm3 of liquid Al3Fe alloy at 1550℃. Compared with the density of 3.7g/cm3 of Zn-55Al, the reason for dross floating is satisfactorily understood.

The geometrical structures and relative stability of the various possible isomers of silicon-oxygen-sulfur oligomers, (SiOS)n (n=1-6), were studied using quantum chemistry calculations. The linear monomer with Si atom bonding to both O and S atoms is the ground state isomer, and the rhombic chains of four-membered rings are the most stable configurations for n=2-4, while the hybrid structures by the 4MRs and hexagonal six-membered ring become energetically most favorable for n=5 and n=6. Vibrational frequency calculations show that the characteristic IR signatures occur at 1290cm 1 for n=1, at the vicinity of 900cm forn=2-4, and at about 1080cm 1 for n=5-6. These distinctive spectra would provide guide for future experimental detections of these small Si-O-S oligomers.

The substituent effect on geometries, energies, frequencies and charge distributions of the various DNA base pair derivatives was evaluated using density functional theory at B3LYP/6-31G* level. The results indicate that the fluorinesubstituted cytosine has great influence over the stabilization energy of the various C∶G derivatives while the nitrosubstituted thymine affects the stabilization energies most deeply among all the A∶T derivatives. The N-H stretching vibrational frequency is red shifted and the shift is almost linear correlated with the N-H bond length elongation. There is no direct relationship between the charge distribution and the stabilization energy.

G-tetrad and other 6-thioguanine (SG) incorporated tetrads have been studied in this Letter. The geometries, energies, charge distributions have been discussed. The effects of different cations (K+ and Na+) on the various tetrads have also been studied. The outcomes show that as the SG number increases the tetrad becomes more and more unstable. The Na+ binds more tightly with the tetrad than that of K+ without hydration correction, while considering hydration effects the stability sequence changes to K+>Na+. Electrostatic potential map of the tetrads have been plotted and the binding sites of cations have been also shown.