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Single transition metal (TM) atoms such as Fe, Co and Ni occupying a carbon divacancy in tetragonal graphene (TG) and bonded with four nitrogen atoms (TM@N4TG) as electrocatalysts are investigated by means of first‐principles calculations. To consider the effect of solvent species on the local configuration of the active single metal, a thermodynamical full‐landscape searching (TFLS) scheme is employed. The calculated thermodynamic overpotentials (ηtd) from our TFLS indicate that Co@N4TG displays high catalytic activity toward both oxygen evolution reaction (OER) and reduction reaction (ORR), with ηtd OER and ηtd ORR as 0.397 and 0.357 V, respectively. Its OER potential cannot be captured if only one four electron reaction loop (FERL) is considered. The actual active pathways do not always turn out to be the reactions starting from the bare site. Our findings demonstrate that TG is a promising support and TM confined TD can be used to design effective and cheap multifunctional electrocatalysts., Doped Tetragonal Graphene (TG) as electrocatalyst? The pre‐adsorption of solvent functional groups (OH, O and OOH) can tune the adsorption strength of species. A thermodynamic full‐landscape searching scheme is proposed where all the possible reactions were considered. Co@N4TG is confirmed to be a favorable bifunctional single‐atom electrocatalyst for both OER and ORR.

In the literature of heterogeneous water-splitting catalytic thermodynamic study, the computational hydrogen electrode (CHE) scheme is used in the majority of the cases. In this scheme, either the bare surface without O and OH decoration or a decorated phase chosen from a surface Pourbaix diagram is employed as a starting point in a four-electron reaction loop (FERL) to describe the oxygen evolution reaction (OER) process. The electrode potential that makes every step of this FERL exothermic is defined as the thermodynamic overpotential (η

The effects of isotropic strains on the magnetic properties in ZnO and GaN induced by cation vacancies are comparatively investigated by density functional theory calculations. The magnetic moments and the couplings between vacancies in different charged states are calculated as a function of strains. The modulation of strain on the magnetic properties relies on the materials and the charge states of cation vacancies in them. As the occurrence of charge transfer in ZnO:V Zn under compression, the coupling between $$V_{\rm{Zn}}^{0} $$ is antiferromagnetic (AFM) and it could be stabilized by strains. Tensions can strengthen the ferromagnetic (FM) coupling between $$V_{\rm{Zn}}^{0} $$ but weaken that of $$V_{\rm{Ga}}^{ - } $$ . The neutral V Ga are always AFM coupling under strains from −6 to +6% and could be stabilized by compressions. The interactions between $$V_{\rm{Ga}}^{ - } $$ are always FM with ignorable variations under strains; however, the FM couplings between $$V_{\rm{Ga}}^{2 - } $$ could be strengthened by compressions. These varying trends of magnetic coupling under strains are interpreted by the band coupling models. Therefore, strain-engineering provides a route to manipulate and design high Curie temperature ferromagnetism derived and mediated by intrinsic defect for spintronic applications.

The effects of isotropic strains on the doping and magnetic properties of nitrogen doped ZnO system are investigated by density functional theory calculations. The formation energy and the ionization energy of N O in ZnO are calculated each as a function of strains. We show that compressive strains favor the solubility of nitrogen in ZnO, while the tensile ones render the acceptor level shallower. The shallower energy level means that the acceptor wave function becomes delocalized, which is favorable for mediating long-range coupling between defects. The effects of strains on the coupling strength between two N O s are also studied. Our calculations indicate that the ferromagnetic coupling in ZnO:N can be enhanced by applying tensile strains, but weakened by compressive strains. These manipulation trends of the magnetic couplings under stains are interpreted by the band coupling models.

The electronic and magnetic properties of the singly charged oxygen vacancy in undoped ZnO under biaxial strains are investigated by density functional theory calculations. A net magnetic moment (MM) of 0.561 μB is obtained for in ZnO under no strains, but the magnetic interaction between them is antiferromagnetic. The formation energy of V O and the MM induced by as well as the coupling type and strength between vary with the application of biaxial strains. Compressive strains can enhance the concentrations of V O and enlarge the MM, and strengthen the antiferromagnetic interactions between them at lower V O concentrations. However, at higher V O concentrations, the coupling varies from sizable antiferromagnetic to negligible weak ferromagnetic, and then becomes paramagnetic with the increase of compression. Antiferromagnetic results are further confirmed by the local density approximation with Hubbard U (LDA + U) calculations.