XCC2--a new coupled cluster model for the second-order polarization propagator

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Modeling

Background:

• Coupled cluster (CC) methods are essential for accurate electronic structure calculations.
• Polarization propagators are crucial for determining molecular properties like polarizability.
• Existing methods like TD-CC2 offer a balance between accuracy and computational cost.

Purpose of the Study:

• Introduce and validate a new coupled cluster model for polarization propagators, termed XCC2.
• Assess the performance of XCC2 for static and dynamic dipole polarizabilities.
• Evaluate the accuracy of XCC2 for dispersion coefficients in molecular complexes.

Main Methods:

• The XCC2 method combines time-independent coupled cluster theory with TD-CC2 excitation operators.
• Calculated static and dynamic dipole polarizabilities for over 20 molecules.
• Computed dispersion coefficients for noncovalent molecular complexes.
• Compared XCC2 results against time-dependent coupled cluster doubles (TD-CCSD) and TD-CC2 benchmarks.

Main Results:

• XCC2 demonstrates a significant reduction in average percent error compared to TD-CC2.
• A 4-fold reduction in mean polarizability error and a 2-fold reduction in anisotropic polarizability error were observed.
• XCC2 yields dispersion coefficients of high quality for molecular complexes.
• The computational cost of XCC2 is comparable to that of TD-CC2.

Conclusions:

• XCC2 provides a practical and accurate alternative to TD-CC2 for calculating molecular properties.
• The method achieves near-CCSD quality for second-order polarization propagators.
• XCC2 offers an improved balance of accuracy and computational efficiency in quantum chemistry.