Double Similarity Transformed Coupled Cluster Theory: Non-Covalent Interactions and Excited State Energetics
The existing ab-initio theories often require high computational scaling to account for the ground and excited state energetics in a quantitatively correct manner. In this talk, I shall propose an inexpensive dual exponential Ansatz based recursive similarity transformed Coupled Cluster methodology, which accurately captures dynamical correlation of weakly correlated molecular systems in an affordable manner. The superior accuracy of the proposed method in describing non-covalent interactions is ensured by the inclusion of high rank correlation effects and a balanced treatment of screened Coulomb interactions. Further, starting with a correlated description of the ground state, I shall propose a Linear Response formulation to describe electronically excited states of isolated gas phase molecules. I will demonstrate how our method strikes the right balance between computational cost and accuracy. The efficacy of the formulation will be demonstrated with a number of numerical examples.