Robust Ferromagnetism in Hexagonal Honeycomb Transition Metal Nitride Monolayer.

Two-dimensional intrinsic magnetic materials with high Curie temperature are promising candidates for next-generation spintronic devices. In this work, we design two kinds of two-dimensional transition metal nitrides, VN and FeN, both with a hexagonal honeycomb lattice. Based on the formation energy, and phonon spectra calculations as well as the molecular dynamics simulations, their structural stability is demonstrated.

Prediction of transition metal carbonitride monolayers MNC (M = Cr, Mn, Fe, and Co) made up of a benzene ring and a planar MN moiety.

Based on first-principles calculations, we predict a class of graphene-like magnetic materials, transition metal carbonitrides MNC (M = Cr, Mn, Fe, and Co), which are made up of a benzene ring and an MN moiety, two common planar units in the compounds. The structural stability is demonstrated by the phonon and molecular dynamics calculations, and the formation mechanism of the planar geometry of MNC is ascribed to the synergistic effect of sp hybridization, M-N coordination bond, and π-d conjugation. The MNC materials consist of only one layer of atoms and the transition metal atom is located in the planar crystal field, which is markedly different from most two-dimensional materials.

Bifunctional electrocatalytic activity of Fe-embedded biphenylene for oxygen reduction and evolution reactions.

Transition metal single-atom catalysts have attracted great attention because of their great potential applications in the chemical industry. Except for graphene, there are few single-layer materials that can act as substrates to support the dispersive metal atoms. Recently, a biphenylene layer, a new two-dimensional allotrope of graphene, was synthesized in experiments, providing a new substrate layer to fabricate single-atom catalysts (SACs).

Interlayer Coupling Induced Sharp Increase of the Curie Temperature in a Two-Dimensional MnSn Multilayer.

The MnSn monolayer synthesized recently is a novel two-dimensional ferromagnetic material with a hexagonal lattice, in which three Mn atoms come together to form a trimer, making it remarkably different from other magnetic two-dimensional materials. Most impressively, there occurs a sharp increase of the Curie temperature from 54 to 225 K when the number of layers increases from 1 to 3. However, no quantitative explanation has been reported in previous studies.

A two-dimensional topological nodal-line material MgN with extremely large magnetoresistance.

Using first-principles calculations, we predict a stable two-dimensional atomically thin material MgN. This material has a perfect intrinsic electron-hole compensation characteristic with high carrier mobility, making it a promising candidate material with extremely large magnetoresistance. As the magnetic field increases, the magnetoresistance of the monolayer MgN will show a quadratic dependence on the strength of the magnetic field without saturation.

Charge transfer effect on Raman shifts of aromatic hydrocarbons with three phenyl rings from ab initio study.

To clarify the charge transfer effect on Raman spectra of aromatic hydrocarbons, we investigate the Raman shifts of phenanthrene, p-terphenyl, and anthracene and their negatively charged counterparts by using density functional theory. For the three molecules, upon charge increasing, the computed Raman peaks generally shift down with the exception of a few shifting up. The characteristic Raman modes in the 0-1000 cm region persist up, while some high-frequency ones change dramatically with three charges transferred.

Ba2phenanthrene is the main component in the Ba-doped phenanthrene superconductor.

We have systematically investigated the crystal structure of Ba-doped phenanthrene with various Ba doping levels by the first-principles calculations combined with the X-ray diffraction (XRD) spectra simulations. Although the experimental stoichiometry ratio of Ba atom and phenanthrene molecule is 1.5:1, the simulated XRD spectra, space group symmetry and optimized lattice parameters of Ba1.

Van der Waals density functional study of the structural and electronic properties of La-doped phenanthrene.

By the first principle calculations based on the van der Waals density functional theory, we study the crystal structures and electronic properties of La-doped phenanthrene. Two stable atomic geometries of La₁phenanthrene are obtained by relaxation of atomic positions from various initial structures. The structure-I is a metal with two energy bands crossing the Fermi level, while the structure-II displays a semiconducting state with an energy gap of 0.

Layered pnictide-oxide Na2Ti2Pn2O (Pn=As, Sb): a candidate for spin density waves.

From first-principles calculations, we have studied the electronic and magnetic structures of compound Na2Ti2Pn2O (Pn=As or Sb), whose crystal structure is a bridge between or a combination of those of high-Tc superconducting cuprates and iron pnictides. We find that in the ground state Na2Ti2As2O is a novel blocked checkerboard antiferromagnetic semiconductor with a small band gap of about 0.15 eV.

Spin wave excitations in AFe1.5Se2 (A = K, Tl): analytical study.

By generalizing the equation of motion method, we can analytically solve the spin wave excitations for the intercalated ternary iron-selenide AFe(1.5)Se(2) (A = K, Tl) in a complex 4 × 2 collinear antiferromagnetic order. It is found that there are one acoustic branch (gapless Goldstone mode) and two gapful optical branches of spin wave excitations with each in double degeneracy.

The effect of the Wyckoff position of the K atom on the crystal structure and electronic properties of the compound KFe₂Se₂.

By means of first-principles electronic structure calculations, we study the effect of the Wyckoff position of the K atom on the crystal and electronic structures of the compound KFe(2)Se(2). When the K atoms take up the Wyckoff positions 2a, 2b and 4c (the related structures of KFe(2)Se(2) are referred to as Struc-2a, Struc-2b and Struc-4c), the calculated lattice constants c lie in the ranges 13.5-14.

Electronic structures and magnetic order of ordered-Fe-vacancy ternary iron selenides TlFe1.5Se2 and AFe1.5Se2 (A=K, Rb, or Cs).

By the first-principles electronic structure calculations, we find that the ground state of the Fe-vacancies ordered TlFe(1.5)Se(2) is a quasi-two-dimensional collinear antiferromagnetic semiconductor with an energy gap of 94 meV, in agreement with experimental measurements. This antiferromagnetic order is driven by the Se-bridged antiferromagnetic superexchange interactions between Fe moments.