All the integrals in the present implementation are generated using density fitting approximation. The integrals of up to two virtual indices are constructed and stored in the memory/disk. The integrals containing three and four virtual are not stored, and the terms involving the contraction of t or r ( l ) amplitudes with integrals with three or four virtual indices are factorized in terms of the three-center two-electron integral( density fitting approximation is only effective in reducing the formal scaling of terms related to Coulomb interactions, and it is not able to reduce the formal scaling of terms related to exchange interactions. However, by using density fitting, the storage requirement for the terms related to exchange interactions can be greatly reduced, resulting in faster calculations due to decreased disk I/O. The tensor-hyper contraction (THC) method of Martinez and co-workers and the chain of sphere exchange (COSX) of Neese and co-workers can reduce the formal scaling of the exchange kind of terms in coupled cluster method. However, such approaches are not considered for the present case.