First Principles Study Of V-adsorbed MoSe₂ Monolayer

Two-dimensional?2D?materials have caught people's eyes on account of their excellent electrical,optical and mechanical properties.Since the increased force on graphene,layered transition metal dichalcogenides?TMDCs?are a new class of Dirac material that have evoked a wave of enthusiasm because of their direct bandgap,about1-2 eV,which makes them attractive for electronic applications than graphene.Compared with the wide research on the single atom adsorbed Mo S₂ monolayer,less attention has been paid to the investigation on the V adsorbed MoSe₂ monolayer.With the method of first-principles calculations,we research the effect of V adatom on the MoSe₂ monolayer,including structure,electron,and magnetism.Meanwhile,adsorption concentration is a part of research because magnetic ground state is associated to it.The results indicate that it is possiple for the V atom to chemically adsorb on the MoSe₂ monolayer and the most stable adsorption position is on top of a Mo atom with three nearest neighbor Se atoms.The forming of V-Se covalent bonds is attributed to the electron transfer.Moreover,it is also related to the hybridization of V with Se and Mo.With a single V adsorbed,several defect states appear in the band gap of pure MoSe₂ monolayer which lead to a magnetic moment of 5m_B,where the V-3d and Mo-4d orbitals are the major contributors.Combining the valence configuration of V adatom with the density of states,the V adatom is in high-spin state.In addition,the crystal field squashes a part of the V-4s electron into the V-3d orbitals leading to the increase of unpaired electrons of d-shell,which gives rise to the enhancement of the local magnetic moment of V atom.We use generalized gradient approximation?GGA?and GGA+U?GGA plus coulomb repulsion?to research the influence of V-V distance on the magnetic ground state.In addition,the exchange integrals of ferromagnetic and antiferromagnetic coupling are estimated.By GGA,the results show that the magnetic ground state is ferromagnetic at the short V-V distance.However,the ferromagnetism gradually weakens and even transfers into antiferromagnetism with the increasing distance between the V adatoms.When the V-V distance is short,the magnetic ground state shows strong ferromagnetism.An exchange mechanism is put forwad which is connected with the on-site exchange on Mo and the hybridization between Mo and V.However,under the influence of increased the V-V distance and the strong electron correlation,the ferromagnetic exchange mechanism is affected,leading to antiferromagnetism,which mainly orginates from the superexchange interaction.