Ruibin Dong

Structural transition of hexagonal tube to rocksalt for (MgO)3n, 2≤n≤10

The structures of (MgO)(3n) (2<or=n<or=10) clusters are studied using density functional theory (DFT). The starting structures are generated from empirical genetic algorithm simulations. The lowest-energy structures of (MgO)(3n) are then obtained from a number of structural isomers by using DFT optimization. It is found that when n<or=5 hexagonal tube is the most stable structure, and when n>or=6 (except 7) the rocksaltlike structure is favored, which is the same as that of the bulk. The n=7 is an interesting case, where the structure again is the hexagonal tube as the most stable structure. However, from the second order difference of the average atomization energy, we find that the n=7 case is thermodynamically unstable with respect to disproportionation to the smaller and larger clusters. The result may be the reason that it is not observed in the experiment. Therefore, we can conclude that the geometry transition really takes place at n=6. The rocksalt is the most stable structure for a large range of n numbers, from the (MgO)(3x6) cluster to bulk magnesium oxide. The result is different from Wilsons previous prediction because of the use of the ionic potential.

Structural, electronic and magnetic properties of AgnFe clusters (n ? 15): local magnetic moment interacting with delocalized electrons

The size-dependent electronic, structural and magnetic properties of AgnFe (n ≤ 15) clusters have been investigated by using the density functional theory (DFT) within the generalized gradient approximation. The starting structures were generated from empirical genetic algorithm simulations. The most stable structures were then selected from a number of structural isomers based on the results of the further DFT calculations. The atom prefers to stay at the centre of the clusters. The 2D to 3D transition occurs at n = 6. The magnetic properties and the geometric structures are strongly correlated. For , the total magnetic moment of the cluster is quenched. The reason is similar to the Kondo effect in bulk metal. Also, is considered to be very stable according to the 18-electron counting rule.

Thermodynamic phase diagram for hydrogen on polar InP(111)B surfaces

Thermodynamic stability of hydrogenated polar InP(111)B surfaces is systematically studied by performing first-principles density functional calculations. Employing a thermodynamic approach, the hydrogen chemical potential is considered as functions of temperature and pressure. The calculated Gibbs free energies demonstrate that the surface structures of InP(111)B strongly depend on growth condition and surface compositions. The (2×2) surfaces with 3PH2+PH3, 3H+PH3, 3H, and P trimer, and the (3×3) surface with In adatom are stable phases under different chemical potentials of P and H, respectively. Moreover, our calculations suggest that the ideal surface and most of (3×3) surfaces are just metastable due to their deviation from electron counting rule. The calculated surface phase diagrams as the functions of temperature and pressure of H2 reveal that the (2×2) surface with P trimer is stable under the experimental growth condition (550–800 K). Once the samples are cooled down in a H-rich ambient, the hyd...

Transport properties of graphene nanoribbon-based molecular devices.

The electronic and transport properties of an edge‐modified prototype graphene nanoribbon (GNR) slice are investigated using density functional theory and Greens function theory. Two decorating functional group pairs are considered, such as hydrogen‐hydrogen and NH2‐NO2 with NO2 and NH2 serving as a donor and an acceptor, respectively. The molecular junctions consist of carbon‐based GNR slices sandwiched between Au electrodes. Nonlinear I‐V curves and quantum conductance have been found in all the junctions. With increasing the source‐drain bias, the enhancement of conductance is quantized. Several key factors determining the transport properties such as the electron transmission probabilities, the density of states, and the component of Frontier molecular orbitals have been discussed in detail. It has been shown that the transport properties are sensitive to the edge type of carbon atoms. We have also found that the accepter‐donor functional pairs can cause orders of magnitude changes of the conductance in the junctions.

First-principles study of atomic and electronic structures of amorphous HgTe

The atomic and electronic structures of amorphous-HgTe have been studied. We created a 128-atom and a 256-atom model structures from the first principle relaxation. The electronic properties are analyzed with electronic density of states. The geometry structures are discussed by RDF. It is shown that the density-functional methods in the generalized gradient approximation predict a band gap of 0.4–0.45 eV for amorphous HgTe, contrary to the negative band gap for crystalline HgTe.