Linear response approach in FSMRCC for molecular property

Multi-reference coupled-cluster (MRCC) method emerged as an efficient tool to describe the electronic structure of degenerate and quasi-degenerate systems. Development of linear response in MRCC frame-work using Lagrange variational technique is the choice of interest for the calculation of molecular properties at the ground state as well as at the electronic excited states. In chapter 1 a general introduction has been given for both single-reference and multi-reference methods. Z-vector technique and Lagrange formulation for SRCC as well as MRCC are presented in this chapter. In chapter 2 CVA-FSMRCCSD theory and the Lagrange formulation have been discussed for open shell doublet molecules and the expressions for first- and second-order energy derivatives are given. Also analytic dipole moments and dipole polarizabilities of Oxygen mono-fluoride and Nitrogen dioxide using CVA-FSMRCCSD method are presented. Chapter 3 and 5 includes CVA-FSMRCCSD method for calculation of excited state properties of closed molecules. Chapter 4 presents hyperpolarizability of open shell molecules.