Quantum Chemical Study On New Superhalogens Based On Different Electron Counting Rules

We systematically studied the electron detachment energy of several types of superhalogens and their performance as low toxicity electrolytes via both ab initio wave function-based method and density functional theory(DFT).The dissertation mainly consists of two parts,a sum of four chapters.In the first part,different types of superhalogen systems were selected as the object of study,the applicability of various exchange-correlation(XC)functionals for these superhalogens systems was carefully tested.In the second part,a theoretical study was performed to explore the new candidates for the high-efficiency and low-toxicity electrolytes of Li-ion batteries baed on non-halogen superhalogens.The first chapter is an introduction that mainly describes the researching background and the meaning of topic,including the principal characteristics and applications of superhalogen as well as the importance of the halogen-free low-toxicity electrolyte materials.In the second chapter,we introduce the utilized theoretical methods,i.e.,the basic concepts and related knowledge of ab initio and DFT methods.In the third chapter,a theoretical study was performed for the applicability of popular XC functionals on the different types of superhalogen systems.The structures of superhalogens selected obey the octet electron counting rule,which cover the ranges from simple mononuclear to complex polynuclear structures as well as from halogen to non-halogen superhalogens.In this chapter,a total number of 17 XC functionals were tested with the high level coupled-cluster single double including perturbative triple excitations(CCSD(T))results as reference.Based on the results,it is clearly shown that four functionals,B2T-PLYP,B2GP-PLYP,B2K-PLYP and the ?B97X are capable of providing reliable results,which approach the accuracy at the CCSD(T)level.In addiation,the influence of various basis sets is quite limited for the DFT study of superhalogens,the basis set influence is usually moderate,in most cases,it is enough to utilize the basis set of triple-? quality.The fourth chapter is another work that explore the potential of 23 halogen-free superhalogen anions as high-performance electrolytes of Li-ion batteries.According to high-level ab initio results at the CCSD(T)level,eight candidates,obeying the Wade-Mingos rule,should be capable of forming electrolytes,which are better than the currently used commercial products.When comparing different methods,MP2 was found to be in good agreement with CCSD(T)in the calculation of parameters,which describing the performance of potential electrolytes.The five functionals selected here(?B97XD,B2GP-PLYP,B2K-PLYP,B2T-PLYP and B3LYP)are also capable of reproducing the variational trends of the relative values of different structures at the CCSD(T)level.However,the actual DFT values of ?ELi+ are usually different from those of CCSD(T)by more than 1 eV,and this point should not be ignored if accurate ?ELi+ values are desired.