First-principles Calculation Study On The Superconductivity Of Li Intercalated SnS₂

As a typical layered s-p metal chalcogenide,tin disulfide（SnS₂）is composed of sulfur element and tin element which are earth-abundant,nontoxic,and environment-friendly.So,SnS₂ has certain advantages and has been aroused interests.Superconductivity is an important macroscopic quantum phenomenon in nature.For the layered materials connected by weak van der Waals（vdW）interaction,intercalation of molecules,atoms,and ions into vdW layers is an effect method to induce the superconductivity.The intercalation and diffusion of Li in SnS₂ interlayer have been investigated by the first-principles approach for the application in lithium-ion battery.The experiments by performing lithium storage tests also proved that SnS₂ can be as an anode material of lithium-ion battery.So,we wonder whether the superconductivity can be induced in the Li-intercalated SnS₂?In this paper,electronic structure,lattice dynamics,and electron-phonon（EP）interaction of Li-intercalated bilayer and bulk SnS₂ are investigated via first-principles calculations.The main research work of this article has two aspects:（1）The superconductivity of Li-intercalated bilayer SnS₂The energetically stable configuration for Li intercalated bilayer SnS₂ is/AB/stacking,which is different from/AA/stacking for pristine bilayer SnS₂.So we conclude that stacking order of bilayer SnS₂ can also be tuned by intercalation,in addition to switch by charging,the external electric field and the pressure in the literature.The inserting Li is energetically favorable to occupy the octahedral interstitial site.The interlayer interaction is changed from the weak vdW-type to the strong coulomb-type,due to the charge transfer from the Li to SnS₂.The softening of acoustic phonon near k high-symmetey point enhances the EP interaction.The obtained EP coupling constant λ is 1.63 and the estimated superconducting temperature T.c can achieve 14.0 K.The calculation of electronic structure shows that the dispersion of bands near the Fermi level has no noticeable change except for the filling of the bottom of the conduction band（i.e.rigid band model）,suggesting that the intercalated Li atoms mainly play a role of charge reservoir and the superconductivity is an intrinsic property as those in Li-intercalated bilayer MoS₂ and bilayer phosphorene.So,we speculate this conclusion may also exist in other intercalated layer compounds,and these findings may promote experimental efforts in search of more quasi-2D superconducors.（2）The superconductivity of Li-intercalated bulk SnS₂The different sizes supercells of bulk SnS₂ are used to simulate different Li concentration of LixSnS₂ compounds.The intercalated Li atom occupies the octahedral interstitial site which is the center of octahedron composed of six S atoms.For LiSnS₂（i.e.1×1×1 primitive cell）,Li0.5SnS₂（i.e.1×1×2 supercell）and Li0.2sSnS₂（i.e.2×2×1 supercell）,they are dynamically unstable,while for Li0.125SnS₂（i.e.2×2×2 supercell）,its dynamic is stable.These results show that the intercalated Li concentration in the bulk SnS₂ should not be too large.For Li0.125SnS₂,we get the EP coupling λ = 0.4 and the estimated Tc = 1.1 k which is far below the Li-intercalated bilayer SnS₂.The reason is that the behavior of softening of acoustic phonons in Li-intercalated bilayer SnS₂is absent in Li intercalated bulk SnS₂.