Weiguang Chen

First-principles investigation of mechanical and electronic properties of MNNi3 (M=Zn, Mg, or Cd)

Mechanical and electronic properties of an antiperovskite-type superconductor ZnNNi3 as well as its isostructural and isovalent counterparts MgNNi3 and CdNNi3 have been studied by using the first-principles calculations. Lattice constant a, bulk modulus B, elastic constants of cubic lattice (C11, C12, and C44), compressibility K, shear modulus G, tetragonal shear modulus G′, effective charges, as well as electronic structures of the three compounds have been calculated. The results show that the lattice constants of the three compounds have a relationship a(ZnNNi3)<a(MgNNi3)<a(CdNNi3), while on the contrary, the order of the bulk modulus is B(CdNNi3)<B(MgNNi3)<B(ZnNNi3), consisting with the tetragonal shear modulus G′. The neighboring Ni and N atoms are prone to form covalent bonds, while the M-Ni/N (M=Zn, Mg, or Cd) favor ionic nature. For the electronic structures, Ni 3d and the hybridization between Ni 3d and N 2p have the most contributions to the total density of states at the Fermi level [N(EF)] for...

Half-metal behaviour mediated by self-doping of topological line defect combining with adsorption of 3d transition-metal atomic chains in graphene

We present a systematic study of 3d transition-metal (TM) atomic chains adsorbed on a line defect consisting of octagonal and pentagonal carbon rings embedded in a perfect graphene sheet. The results suggest that Sc, Ti, V, Cr and Mn atoms can be spontaneously adsorbed at octagonal sites and form an atomic chain along the line defect in graphene, while Fe, Co and Ni atomic chains are adsorbed at pentagonal sites. Moreover, the Sc, Ti, V, Cr, Mn and Fe chains embedded in line defect of graphene structures show half-metallic characters. These results propose a new route to explore the potential applications of the system in spintronic devices.

Electronic and Magnetic Properties Modulated by Adsorption of 3d Transition Metal Atoms in Monolayer and Bilayer MoS2 Sheets

The adsorption effects of 3d transitional metal (TM) adatoms on electronic and magnetic properties of monolayer and bilayer MoS2 sheets have been investigated by using first-principle calculations based on the density functional theory. The calculated results suggest that both monolayer and bilayer MoS2 sheets have power abilities of absorbing 3d TM atoms. The interlayer adsorption of bilayer MoS2 is relatively more stable than the surface adsorption of monolayer MoS2. The 3d TM adatoms and the neighboring S atoms behave a clear covalent-binding character. It was found that TM adatoms induce certain impurity states within the band gap of the pristine MoS2 sheet which result in the systems magnetically semiconducting or half metallic. The adsorbed systems for Cr and Co on the surface of monolayer MoS2 sheet, as well as Sc, Cr and Fe in the interlayer of bilayer MoS2 sheet exhibit half-metallic behavior. And the other 3d TM-adsorbed systems are magnetic semiconductor except for Ni species.

Effects of vdW Interaction and Electric Field on Friction in MoS2

AbstractnSliding behaviors between two MoS2 layers have been investigated using DFT calculations including vdW dispersion. Contribution of vdW interactions to energy corrugations and maximum lateral frictional forces of the sliding system has been calculated. Our investigations show that the smaller the external normal load is, the larger the contribution of vdW interaction to the friction is. The energy corrugation and lateral frictional force as a function of the electric field are derived, suggesting that friction can be reduced by an external electric field. The reduced friction is attributed to a weaker chemical interaction enabled by the charge depletion between the adjacent S planes. In-depth understanding of the relationship between friction and interlayer interaction shows that friction can be tuned by external electric fields.n

Van der Waals Effects on semiconductor clusters

Van der Waals (vdW) interactions play an important role on semiconductors in nanoscale. Here, we utilized first‐principles calculations based on density functional theory to demonstrate the growth mode transition from prolate to multiunit configurations for Gen (nu2009=u200910–50) clusters. In agreement with the injected ion drift tube techniques that “clusters with nu2009<u200970 can be thought of as loosely bound assemblies of small strongly bound fragments (such as Ge7 and Ge10),” we found these stable fragments are connected by Ge6, Ge9, or Ge10 unit (from bulk diamond), via strong covalent bonds. Our calculated cations usually fragment to Ge7 and Ge10 clusters, in accordance with the experiment results that the spectra Ge7 and Ge10 correspond to the mass abundance spectra. By controlling a germanium cluster with vdW interactions parameters in the program or not, we found that the vdW effects strengthen the covalent bond from different units more strikingly than that in a single unit. With more bonds between units than the threadlike structures, the multiunit structures have larger vdW energies, explaining why the isolated nanowires are harder to produce.

Thickness dependent of phase shift between surface energy and work function in Pb ultrathin films

Through first-principles calculations within density functional theory, the phase shift between surface energy and work function in FCC (111) and HCP (0001) Pb and Pb1–xBix alloy films has been investigated. Deviating from the previously described phase mismatch between the surface energy and work functions, an additional phase shift of about one monolayer is identified at small thickness of the Pb and Pb alloy films. The additional phase shift depends on the film thickness and will disappear as thickness increases. Moreover, we give an interpretation of the one-monolayer deviation in the framework of the free electron model, attributing it to the unique structure of the Fermi surface in Pb ultrathin films.

First-principles investigation of C60 molecule adsorption on a diamond (1 0 0)-2 × 1 surface

Using first-principles calculations based on density functional theory, we have systematically studied the geometric and electronic properties of a C60 molecule adsorbed on a diamond (1?0?0)-2 ? 1 surface. The results show that the C60 molecule is energetically favored when adsorbed on both trench sites over four dimers (T4) and row sites over two dimers (R2) and the most energetically favored adsorption configuration is that in which a hexagon ring of C60 binds to a dimer of the row sites (R1), i.e. R1(e), which has a very large distortion forming three pores with a maximum opening width of 3.84??. According to our simulations, we found that the adsorption properties are closely related to the local structure of C60 around the binding sites, the geometric deformations of C60 and the substrate, and the number of dangling bonds on the substrate. The calculated electronic structures of some stable adsorption configurations further reveal that by altering the orientation of the adsorbed C60 molecule on the diamond (1?0?0) surface the system with semiconductor properties may turn into one with metallic characteristics.