Static polarizabilities for excited states within the spin-conserving and spin-flipping equation-of-motion coupled-cluster singles and doubles formalism: Theory, implementation, and benchmarks

• Published in: The Journal of chemical physics 2016-11, Vol.145 (20), p.204116-204116
• Main Authors: Nanda, Kaushik D., Krylov, Anna I.
• Format: Article
• Language: English
• Subjects: Amplitudes; Charge transfer; Clusters; Electron spin; Electron states; Formalism; Lagrange multiplier; Mathematical analysis; Molecular orbitals; Uracil; Wave functions
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.4967860

We present the theory and implementation for calculating static polarizabilities within the equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) framework for electronically excited states and its spin-flip variant. We evaluate the second derivatives of the EOM-CCSD Lagrangian with respect to electric-field perturbations. The relaxation of reference molecular orbitals is not included. In our approach, the wave function amplitudes satisfy the 2n + 1 rule and the amplitude-response Lagrange multipliers satisfy the 2n + 2 rule. The new implementation is validated against finite-field and CCSD response-theory calculations of the excited-state polarizabilities of pyrimidine and s-tetrazine. We use the new method to compute static polarizabilities of different types of electronic states (valence, charge-transfer, singlets, and triplets) in open- and closed-shell systems (uracil, p-nitroaniline, methylene, and p-benzyne). We also present an alternative approach for calculating excited-state static polarizabilities as expectation values by using the EOM-CCSD wave functions and energies in the polarizability expression for an exact state. We find that this computationally less demanding approach may show differences up to ∼ 30 % relative to the excited-state polarizabilities computed using the analytic-derivative formalism.