First-principles Study On The Adsorption Of Alkali Metal Atoms By Black Phosphorus And Graphyne

The successful preparation of graphene and its excellent physical properties have attracted more and more attention and interest in the field of two-dimensional?2D?materials.2D materials,as well as some other low-dimensional materials exhibit some characteristics that are not available in their corresponding bulk materials owing to quantum confinement effect.At the same time,new members of 2D materials are also emerging such as black phosphorus?BP?,hexagonal boron nitride,transition metal dichalcogenides,silicene,graphdiyne and so on,greatly expanding the research horizon of 2D materials.In this thesis,the first-principle calculation method is adopted to study BP and graphdiyne,and the effects of adsorption of alkali metals on the physical properties of these two materials are also investigated,which may provide some useful references for practical applications in the future.The main research contents and conclusions are in the following:?1?Study the influence of adsorption of alkali metals and layer dependence of BP on the band structure of the adsorption system.Theoretical calculations show that alkali metals tend to adsorb on the hollow?H?site which is energetically preferable.The band gap of BP will gradually decrease with the increase of adsorption concentration of alkali metals.For monolayer and bilayer BP,the system is still a direct band gap semiconductor after the adsorption of alkali metals.Potassium?K?and rubidium?Rb?atoms have almost the same modification of the band gap of monolayer and bilayer BP.Next,the case of K atom adsorbed on trilayer BP is investigated.The results indicate that the band gap of BP will reduce continuously until it is zero when band inversion occurs as the adsorption concentration of K atom increases,causing the transition of BP from a semiconductor to a semimetal.The results show that the charge transfer between alkali metals and the surface of BP produces a local electric field,which regulates the band structure of BP.?2?Investigate the lithium?Li?storage capacity of N-doped graphdiyne?C22N4?.Firstly,different stacking structures are built based on the monolayer graphdiyne and the energy differences between them are compared in order to find the most stable stacking mode.Then,different adsorption sites of Li atom in monolayer graphdiyne are considered and corresponding adsorption energies are compared.Finally,the maximum Li storage capacity of bulk graphdiyne is evaluated based on the most stable bulk structure.The outcomes disclose that,among different stacking modes of graphdiyne,the energy of AA stacking is 7.45 meV/atom higher than that of AB stacking,while the energy of ABC stacking is 1.4 meV/atom slightly lower than that of AB stacking.Considering the subtle energy difference between AB stacking and ABC stacking and calculation cost,we choose AB stacking structure in the following calculations.In the monolayer graphdiyne,the Li atom tends to bond to the N atom and the adsorption energy is-1.776 eV meaning that the adsorption is the most stable.In the process of AB stacking structure adsorbing Li atoms,we found that the Li atoms preferentially bond to two N atoms in the upper and lower layers of bulk structure,respectively.When the fourth Li atom is adsorbed,all Li atoms in the system bond to two N atoms in the upper and lower layers,having the same orientation.As the number of adsorbed Li atoms increases,when the seventh Li atom is adsorbed,Li atom still bonds to the two N atoms in the upper and lower layers,but the orientation is changed.Finally,our calculations show that the maximum Li storage capacity of AB stacking graphdiyne is586.29 mAhg^-1,which is consistent with the experimental results.