The band structures of a new two-dimensional triangle-shaped array geometry of 4340 steel cylinders of square cross section in an epoxy resin were studied by the plane-wave expansion and supercell calculation method. The band gaps of this type of phononic crystals with different defects were calculated such as defect-free, 60 crystal linear defect states, 120 crystal linear defect states, and 180 crystal linear defect states. It was found that the band gap will emerge in different linear defects of the phononic crystals and the bandwidth of linear defect states is larger than that of the free-defect crystal by about 2.14 times within the filling fraction F = 0.1-0.85. In addition, the influence of the filling fraction on the relative width of the minimum band gap is discussed.
The electronic structures and magnetic properties of(Mn, N)-codoped Zn O are investigated by using the firstprinciples calculations. In the ferromagnetic state, as N substitutes for the intermediate O atom of the nearest neighboring Mn ions, about 0.5 electron per Mn2+ion transfers to the N2-ion, which leads to the high-state Mn ions(close to +2.5)and trivalent N3-ions. In an antiferromagnetic state, one electron transfers to the N2-ion from the downspin Mn2+ion,while no electron transfer occurs for the upspin Mn2+ion. The(Mn, N)-codoped Zn O system shows ferromagnetism,which is attributed to the hybridization between Mn 3d and N 2p orbitals.
The dissociation of H_2 molecule is the first step for chemical storage of hydrogen, and the energy barrier of the dissociation is the key factor to determine the kinetics of the regeneration of the storage material. In this paper, we investigate the hydrogen adsorption and dissociation on Mg-coated B_(12)C_6N_6. The B_(12)C_6N_6 is an electron deficient fullerene, and Mg atoms can be strongly bound to this cage by donating their valance electrons to the virtual 2p orbitals of carbon in the cluster. The preferred binding sites for Mg atoms are the B_2C_2 tetragonal rings. The positive charge quantity on the Mg atom is 1.50 when a single Mg atom is coated on a B_2C_2 ring. The stable dissociation products are determined and the dissociation processes are traced. Strong orbital interaction between the hydrogen and the cluster occurs in the process of dissociation, and H_2 molecule can be easily dissociated. We present four dissociation paths, and the lowest energy barrier is only 0.11 eV, which means that the dissociation can take place at ambient temperature.
