Electronic structure of the $LiTiS_2$ and $α-NaFeO_2$ structure $LiTiO_2$ have been investigated using discrete variational Xa molecular orbital method. The $α-NaFeO_2$ structure is the equilibrium structure for $LiCoO_2$, which is widely used in application of lithium second battery. This study especially focused on the charge state of Li and the magnitude of covalency around a Li atom. The average voltage of lithium intercalation also calculated using pseudopotential method, and is known as, the average intercalation voltage of $LiTiO_2(2.19V)$ is higher than that of $LiTiS_2(1.91V)$. This can be explained by the differences in Mulliken charge of lithium atom and the bond overlap population between intercalated lithium and anion in both hosts. The Mulliken charge, which means the ionicity of Li atom was approximately 0.1 in $LiTiS_2$ and the bond overlap populatin(BOP), the covalency between Li and S was about 0.426. Those mean that the intercalated lithium atom is exist as a neutral atom rather than $Li^+$ ion in $LiTiS_2$. In contrast, the Mulliken charge of lithium atom was about 0.7 and the BOP between lithium and oxygen was 0.20 in $LiTiO_2$. Because of this high ionicity and weak interaction between lithium and host material, $LiTiO_2$ has a higher intercalation voltage than the $LiTiS_2$.
호스트 물질인 $TiS_2$ 와 $TiO_2$ 와 여기에 리튬이 삽입 되었을 경우의 전자 상태에 대해 알아 보았다. 특히 삽입된 Li 원자의 전하 상태와 리튬 삽입에 의해 호스트 물질의 화학 결합이 어떻게 바뀌는지에 초점을 맞추었다. 그리고 이를 바탕으로 두 물질의 전지전압(OCV) 차이를 해석 하였다. 전자 상태 계산을 위해서는 DV-Xα 분자궤도 계산법을 이용 하였고, OCV 계산은 VASP(Vienna Ab-initio Simulation Package)를 이용 하였다. 전지전압은 알려진 것과 같이 $LiTiO_2$ 가 $LiTiS_2$ 보다 높게 나왔는데, 이는 $LiTiO_2$ 에서 리튬이온이 높은 이온성을 갖고, 호스트 물질과 상호작용이 적다는 것으로 설명될 수 있다.
