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The development of a quadratic unitary coupled-cluster singles and doubles(qUCCSD) based self-consistent polarization propagator method is reported. Wepresent a simple strategy for truncating the commutator expansion of the UCCtransformed Hamiltonian $\bar{H}$. The qUCCSD method for the electronicground-state includes up to double commutators for the amplitude equations andup to cubic commutators for the energy expression. The qUCCSD excited-stateeigenvalue equations include up to double commutators for the singles-singlesblock of $\bar{H}$, single commutators for the singles-doubles anddoubles-singles blocks, and the bare Hamiltonian for the doubles-doubles block.Benchmark qUCCSD calculations of the ground-state properties and excitationenergies for representative molecules demonstrate significant improvement ofthe accuracy and robustness over the previous UCC3 scheme derived usingM{\o}ller-Plesset perturbation theory.

Unitary coupled-cluster based self-consistent polarization propagator theory: a quadratic unitary coupled-cluster singles and doubles scheme