Benchmarking third-order cluster perturbation theory for electronically excited states.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Spectroscopy

Background:

• Accurate calculation of electronically excited states is crucial for understanding molecular properties and reactivity.
• Coupled cluster (CC) methods, such as coupled cluster singles and doubles (CCSD), are widely used but computationally expensive.
• Cluster perturbation (CP) theory offers a potentially more efficient approach by adding perturbative corrections to a simpler reference calculation.

Purpose of the Study:

• To comprehensively benchmark the reliability of cluster perturbation (CP) theory for calculating electronically excited states.
• To evaluate the accuracy of the third-order CPS(D-3) model, which targets coupled cluster singles and doubles (CCSD) properties.
• To compare the performance of CPS(D-3) against established wavefunction methods.

Main Methods:

• Application of the CPS(D-n) model, where perturbative corrections up to order n are added to coupled cluster singles (CCS) calculations.
• Focus on the third-order CPS(D-3) model for calculating excitation energies.
• Comparative analysis across a diverse set of molecules and various wavefunction methods.

Main Results:

• The CPS(D-3) model demonstrates reliability as an alternative to CCSD for excitation energy calculations.
• CPS(D-3) systematically overestimates excitation energies when compared to higher-level methods like CC3.
• The study provides a thorough evaluation of CPS(D-3)'s accuracy, highlighting its strengths and limitations.

Conclusions:

• CPS(D-3) is a promising and reliable method for calculating electronically excited states, offering a balance between accuracy and computational cost.
• Further development directions for CP theory can be inferred from the observed overestimation compared to high-level CC methods.
• The benchmark study validates CP theory's potential for future applications in computational chemistry.