S. F. Li

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...

Size- and charge-dependent geometric and electronic structures of Bin (Bin−) clusters (n=2–13) by first-principles simulations

Neutral and negatively charged bismuth clusters, Bi n and Bi(-)n (n=2-13), are investigated by first-principles simulations with the scalar-relativistic projector-augmented wave potential and the spin-polarized generalized gradient approximation. Both types of clusters show size-dependent odd-even oscillations in stability, density of states, and vertical and adiabatic electron affinities, in close agreement with experiment. The negative charge thoroughly reverses the oscillations and considerably influences the geometric structures, particularly of the odd-sized clusters. We note that most atoms in the ground states and the low-lying isomers are three coordinated with a quasilayerlike growth mode based on pentagon units, due to a weak s-p hybridization. The Bi12 cluster is found to prefer a small elongated tubelike structure with the surface consists of six curved-pentagon rings and two triangular facets, which may be the basis for the formation of bismuth nanotubes experimentally reported.

An oxidized magnetic Au single atom on doped TiO2(110) becomes a high performance CO oxidation catalyst due to the charge effect

Catalysis using gold nanoparticles supported on oxides has been under extensive investigation for many important application processes. However, how to tune the charge state of a given Au species to perform a specific chemical reaction, e.g. CO oxidation, remains elusive. Here, using first-principles calculations, we show clearly that an intrinsically inert Au anion deposited on oxygen-deficient TiO2(110) (Au@TiO2(110)) can be tuned and optimized into a highly effective single atom catalyst (SAC), due to the depletion of the d-orbital by substrate doping. Particularly, Ni- and Cu-doped Au@TiO2 complexes undergo a reconstruction driven by one of the two dissociated O atoms upon CO oxidation. The remaining O atom heals the surface oxygen vacancy and results in a stable bow-shaped surface “O–Au–O” species; thereby the highly oxidized Au single atom now exhibits magnetism and dramatically enhanced activity and stability for O2 activation and CO oxidation, due to the emergence of high density of states near the Fermi level. Based on further extensive calculations, we establish the “charge selection rule” for O2 activation and CO oxidation on Au: the positively charged Au SAC is more active than its negatively charged counterpart for O2 activation, and the more positively charged the Au, the more active it is.

Intrinsic spin dependent and ferromagnetic stability on edge saturated zigzag graphene-like carbon-nitride nanoribbons

Using first-principles calculations, we have investigated the electronic and magnetic properties of zigzag graphene-like carbon-nitride nanoribbons (Zg-CNNRs) with mono- and dihydrogen-terminated edges asymmetrically. The results demonstrate that spin-down channel completely dominates the states adjacent Fermi level, which is an intrinsic feature and can be accounted for the valence band maximum derived from the nonbonding N-(px,py) orbitals, instead of the bonding C/N-pz π state. Importantly, ferromagnetic ordering is found to be preferred and the magnetism is entirely localized on the N sites of saturated edge due to its stronger electronegativity. Additionally, various edge saturations are further proposed to try to enhance the ferromagnetic ordering and to manipulate the magnetism distributions of Zg-CNNRs.