Using the first-principles full-potential linearized augmented plane-wave method based on density functional theory, we have investigated the electronic structure and magnetism of hypothetical $M$C ($M=\mathrm{Mg}$, Ca, Sr, and Ba) compounds with the zinc-blende (ZB) crystal structure. It is shown that ZB $\mathrm{CaC}$, $\mathrm{SrC}$, and $\mathrm{BaC}$ are half-metallic ferromagnets with large half-metallic gaps (up to $0.83\mathrm{eV}$). The half metallicity is found to be robust with respect to the lattice compression and is maintained up to the lattice-constant contraction of 14%, 13%, and 9% for $\mathrm{CaC}$, $\mathrm{SrC}$, and $\mathrm{BaC}$, respectively. The exchange interactions in these compounds are studied using the augmented spherical wave method in conjunction with the frozen-magnon approach. The Curie temperature is estimated within both the mean field approximation and the random phase approximation. The predicted Curie temperatures of all three half-metallic compounds considerably exceed the room temperature. The large half-metallic gaps, the robustness of the half metallicity with respect to the lattice contraction, and the high Curie temperatures make these systems interesting candidates for applications in spintronic devices. The absence of the transition-metal atoms makes these compounds important model systems for the study of the origin and properties of the half-metallic ferromagnetism of $s\text{−}p$ electron systems.

We performed a systematic full-potential density functional theory study with the generalized gradient and local density $\text{approximation}+U$ approaches on five possible $(1\times 1)$ terminations of the low-index polar (111) surface of ${\mathrm{Fe}}_3{\mathrm{O}}_4$. Applying the concepts of first-principles thermodynamics, we analyze the composition, the structure, and the stability of the ${\mathrm{Fe}}_3{\mathrm{O}}_4$ (111) orientation at equilibrium with an arbitrary oxygen environment. The densities of states of the unrelaxed and relaxed ${\mathrm{Fe}}_3{\mathrm{O}}_4$ (111) surfaces were calculated and compared with that of bulk ${\mathrm{Fe}}_3{\mathrm{O}}_4$. The calculations reveal that the ${\mathrm{Fe}}_{\mathrm{oct}2}\text{−}{\mathrm{Fe}}_{\mathrm{tet}1}\text{−}\mathrm{O}1$-terminated surface is energetically favored, showing metallic properties. The ${\mathrm{Fe}}_{\mathrm{oct}1}\text{−}\mathrm{O}2$-terminated surface is more active than the other two Fe-terminated surfaces, showing half-metallic properties, similar to bulk ${\mathrm{Fe}}_3{\mathrm{O}}_4$. The ${\mathrm{Fe}}_{\mathrm{tet}1}\text{−}\mathrm{O}1$-terminated surface, the O-terminated surfaces, and the surfaces with vacancy defects all show metallic properties.

We presented a theoretical study on the spin-polarized transport of one single-molecule magnet. The results show it has spin filter behavior, and can also be used as a molecular spin valve with large abnormal magnetoresistance, which is an excellent candidate for spintronics of molecular devices. It is also found that the steplike features with negative differential resistance in the $I\text{-}V$ curve indeed originate from the discreteness and narrow features in the density of states of the molecular levels.

Single-layer transition metal dichalcogenides (TMDCs) are showing promising thermoelectric applications due to their superior stability and electronic transport properties. Unfortunately, the intrinsic high lattice thermal conductivity prevents their further improvement of thermoelectric performance. Motivated by recent experimental synthesis of two-dimensional TMDC heterostructures and superlattices, we propose to minimize the lattice thermal conductivity of single-layer MoS₂ and MoSe₂ using the lateral superlattice (LS) as building blocks. First-principles calculations with the phonon Boltzmann transport equation reveal a remarkably low lattice thermal conductivity of MoS₂-MoSe₂ LS due to the enhanced anharmonic phonon scattering as compared to the individual single-layer. We also show that the strong phonon anisotropy of MoS₂-MoSe₂ LS is primarily ascribed to the out-of-plane quadratic acoustic branch and orientation-dependent anharmonic scattering. Our calculations clearly demonstrate the advantages of LS structure in minimizing the lattice thermal conductivity of single-layer TMDCs and also accelerate their related applications in the field of renewable energy.

The spin-polarized transport in a single-molecule magnet Fe4 sandwiched between two gold electrodes is studied, using nonequilibrium Green's functions in combination with the density-functional theory. We predict that the device possesses spin filter effect (SFE), spin valve effect (SVE), and negative differential resistance (NDR) behavior. Moreover, we also find that the appropriate chemical ligand, coupling the single molecule to leads, is a key factor for manipulating spin-dependent transport. The device containing the methyl ligand behaves as a nearly perfect spin filter with efficiency approaching 100%, and the transport is dominated by transmission through the Fe4 metal center. However, in the case of phenyl ligand, the spin filter effect seems to be reduced, but the spin valve effect is significantly enhanced with a large magnetoresistance ratio, reaching 1800%. This may be attributed to the blocking effect of the phenyl ligands in mediating transport. Our findings suggest that such a multifunctional molecular device, possessing SVE, NDR and high SFE simultaneously, would be an excellent candidate for spintronics of molecular devices.