CCSD-PCM: improving upon the reference reaction field approximation at no cost.

Area of Science:

• Computational chemistry
• Quantum chemistry
• Theoretical chemistry

Background:

• Coupled cluster (CC) methods combined with the polarizable continuum model (PCM) for solvation calculations are computationally demanding.
• The standard PTED (perturbation theory energy and density) scheme exhibits nonlinear dependence on CC density, increasing computational cost.

Purpose of the Study:

• To develop computationally efficient approximations for CC-PCM calculations.
• To reduce the significant energy differences between the computationally inexpensive PTE (perturbation theory energy) scheme and the accurate PTED scheme.

Main Methods:

• Introduction of two intermediate approximations: PTE(S) and PTES.
• PTE(S) adds an energy correction to the PTE free energy.
• PTES incorporates explicit PCM terms into the iterative solution of CC equations.

Main Results:

• PTE(S) offers a small improvement over the PTE free energy.
• PTES recovers 50%-80% of the difference between the PTED and PTE schemes.
• The computational cost of PTES is comparable to gas-phase CC calculations.

Conclusions:

• PTE(S) and PTES provide computationally efficient strategies for CC-PCM calculations.
• PTES is a promising approach for achieving CC-quality calculations in solution at a reduced cost.
• The study presents the necessary theoretical expressions and numerical validation for CC-PTE(S) and CC-PTES methods.