The structural stability, electronic and magnetic properties of semihydrogenated graphene and monolayer boron nitride (H-Gra@BN) composite system are studied by the first principles calculation. First, for the six possible stacked configurations of H-Gra@BN in three kinds of magnetic coupling manners, including the nonmagnetic, ferromagnetic and antiferromagnetic, the geometry optimization structures are calculated. The formation energies (Ef) are -28, -37, -40, -35, -28, and -34 meV/atom for AA-B, AA-N, AB-B, AB-B-H, AB-N and AB-N-H configurations of H-Gra@BN, respectively. The details of the six H-Gra@BN configurations are presented. The results show that the AB-B configuration of H-Gra@BN system is most stable with the largest formation energy in the six configurations. Its thickness is the smallest in all six configurations. The formation energies of all configurations are very close to each other and show that the combination of the interlayer between layers is very weak, The interaction between H-Gra and monolayer BN is van der Waals binding. Second, the band structure, total density of states (TDOS), partial density of states and polarization charge density of the most stable H-Gra@BN system are systematically analyzed. This material is ferromagnetic semiconductor. The band gaps for majority and minority spin electrons are 3.097 eV and 1.798 eV, respectively. Each physical cell has an about 1 μB magnetic moment, which is mainly derived from the contribution of the unhydrogenated C2 atom. Furthermore, while the pressure is applied along the z direction, we analyze the TDOS and band structure of H-Gra@BN system, and find that when the z axis strain is more than -10.48% (Δh=-0.45 Å), the valence band maximum of minority spin moves down. The conduction band minimum of minority spin moves from the high symmetry Γ position into a position between Γ and K. The electronic properties of the most stable H-Gra@BN system change from magnetic semiconductor into half metal. When the strain is increased by more than -11.65% (Δh=-0.5 Å), the most stable H-Gra@BN changes into a nonmagnetic metal. To analyze the effect caused by different strains, we analyze the difference in three-dimensional charge density, and find that with the decrease of the layer spacing, the interlayer interaction gradually increases and shows the obvious covalent bond characteristics. This paper predicts a new type of two-dimensional material of which the electronic and magnetic properties can be easily tuned by pressure, and it is expected to be used in nano-devices and serve as an intelligent building material.

Using the density functional theory (DFT) with both the generalized gradient approximation (GGA) and HSE06 hybrid functional calculation, we have investigated the structural and electronic properties of hydrogenated bilayer silicene. Results show that the hydrogenated bilayer silicene may have three configurations: AA-chair-like, AB-chair-like and AA-boat-like forms; after hydrogenation the material properties change from zero band gap semimetal into an indirect band gap semiconductor with forbidden band widths of 1.208, 1.437, and 1.111 eV. We have performed a hybrid HSB06 functional calculation and the correction for the band gaps: 1.595, 1.785, and 1.592 eV. Further analysis of the hydrogenated bilayer silicene with a strained band gap, the relationship between strain and the band gap can be continuously adjusted. Possible applications may be found in future nano-electronic devices.

The structural and electronic properties of spinel LiMn2O4 and its Al doping system LiAl0.125Mn1.875O4 are investigated within the density functional theory in both the generalized gradient approximation (GGA) and the GGA with Hubbard U correction (GGA+U). The results from the GGA method suggest that LiMn2O4 has a cubic structure and the valences of Mn ions are all +3.5, which is unable to explain the Jahn-Teller distortions in the material. The band structure of LiMn2O4 predicted by the GGA method is also inconsistent with experimental result. With the GGA+U method, the low temperature structures of LiMn2O4 and its Al doping system LiAl0.125 Mn1.875O4 are shown to be orthogonal, the two different valence states of Mn, i.e., Mn3+/Mn4+ ions, are then determined, which is then able to explain the Jahn-Teller distortion in octahedron Mn3+O6 and the non-existence of distortion in octahedron Mn4+O6. These results are in good accordance with experimental data. Their band structures by GGA+U calculations are also consistent with experimental results. The GGA+U calculations on the LiAl0.125Mn1.875O4 indicate that with the replacement of an Mn by Al, the crystal structure and electronic properties are not significantly changed, but the Jahn-Teller distortion in octahedron Al3+O6 can be effectively eliminated, which could improve the performance of the anode materials based on LiMn2O4. The phenomenon is in consistent with the electrochemical experiments.

The magnetic and electronic properties of fluorographene doped with M (M=B, N, P, Si) atoms are studied by employing the first principles calculation based on the spin-polarized density functional theory. The results show that the fluorographene doped with B (or P) atoms can cause the semiconductor-to-metal transitions and the fluorographene with doped N (or Si) atoms is still the semiconductor; the substitutional B, P, and N atoms induce magnetic moments of adjacent carbon atoms. For Si atoms doped fluorographene sheet, semiconductor properties keep unchanged, but the band gap changes.

The structural and electronic properties of hydrogenated bilayer boron nitride (BN) were studied by employing the first-principles calculations. Six major polymorphic structures of hydrogenated bilayer BN are considered. Calculated results show that, among them, the AB-BN and AA-BN structures are the most stable ones. The analysis on the energy bands and electronic properties of the two most stable structures are then performed. Structures of AB-BN and AA-BN are both semiconducting with direct band gaps, and the gaps are 1.47 eV and 1.32 eV, respectively, calculated using the GGA method. Since GGA usually severely underestimates the band gap, the hybrid density functional calculations are then conducted, which suggests that the band gaps are 2.52 eV and 2.34 eV for AB-BN and AA-BN structures, respectively. In the most stable structures of AB-BN and AA-BN, B-N bonds show mainly covalent characters, while B-H and N-H bonds exhibit clear ionic characteristics. Moreover, the band gap of hydrogenated bilayer BN atomic sheet can be continuously modulated by biaxial strains. When the lattice constant is compressed by around 8%, the electronic character of the atomic sheet changes from semiconducting into metallic.