RESUMEN
A strong built-in electric field, high carrier mobility and a wide range of optical absorption values are the key parameters for photocatalysts used in water splitting. The design and preparation of photocatalysts possessing simultaneously these characteristics have always been the main tasks in the water splitting field. Here, we report a new family of 2D Na-based photocatalysts, NaAB2 (A = Al, Ga, In; B = S, Se, Te) monolayers, which may achieve this goal. First-principles calculations show that most of the NaAB2 monolayers are semiconductors with a suitable direct band gap ranging from visible to near-infrared light, exhibiting good optical absorption. The electron mobilities of the NaAB2 monolayers are up to 103 cm2 V-1 s-1, meaning the rapid migration of electrons can promote photocatalytic overall water splitting. Importantly, the electrostatic potential differences between the top surface and the bottom surface are larger than 1.23 eV for all the studied NaAB2 monolayers, meaning a high intrinsic built-in electric field that is present in these Na-based photocatalysts can promote the overall water splitting irrespective of their band gaps and band edges. Our studies show that the NaAB2 monolayers may be ideal photocatalysts for use in water splitting and may initiate a new round of experimental studies.
RESUMEN
We investigate the electronic structures and electronic transport properties of zigzag phosphorene nanoribbons with oxygen-saturated edges (O-zPNRs) by using the spin-polarized density functional theory and the nonequilibrium Green's function method. The results show that the O-zPNR is an antiferromagnetic (AFM) or ferromagnetic (FM) semiconductor with spins localized at two ribbon edges anti-parallel or parallel with each other. The electronic transmission for the single AFM or FM O-zPNR is zero when a bias voltage is applied to the two electrodes made of the same type O-zPNR. Nonzero transmission arises for the AFM-AFM and FM-FM O-zPNR heterojunctions. The transmission spectrum and the electrical current are fully spin polarized for the FM-FM O-zPNR heterojunction. An in-plane transverse electrical field can effectively manipulate the electronic structure and spin-dependent electronic transport. It induces splitting of the spins of the two edges and makes the AFM O-zPNR become a half metal. Moreover, the transverse electrical field gives rise to the transmission spectrum and the spin polarized electrical current for the AFM-AFM O-zPNR heterojunction. The degree of spin polarization can be tuned by the strength of the transverse field.
RESUMEN
We have studied the electronic structures and magnetism of SrFeO2 under pressure by first-principles calculations in the framework of density functional theory (DFT) with GGA+U and HSE06 hybrid functionals, respectively. The pressure-induced spin transition from S = 2 to S = 1 and the antiferromagnetic-ferromagnetic (AFM-FM) transition observed in experiment are well reproduced by taking the site repulsion U and its pressure dependence into account. The electronic structure and its change with the pressure can be qualitatively understood in an ionic model together with the hybridization effects between the Fe 3d and O 2p states. It is found that the pressure leads to a change in Fe 3d electronic configuration from (d(z(2)))(2)(d(xz)d(yz))(2)(d(xy))(1)(d(x(2)-y(2)))(1) under ambient conditions to (d(z(2)))(2)(d(xz)d(yz))(3)(d(xy))(1)(d(x(2)-y(2)))(0) at high pressure. As a result, the spin state transits from S = 2 to S = 1 and both the antiferromagnetic intralayer Fe-O-Fe superexchange interaction and the interlayer Fe-Fe direction exchange coupling at ambient pressure become ferromagnetic at high pressure according to the Goodenough-Kanamori (G-K) rules. Additionally, our calculations predict another spin transition from S = 1 to S = 0 at pressures of about 220 GPa.