Coupled-cluster method tailored by configuration interaction

Area of Science:

• Computational chemistry
• Quantum chemistry
• Theoretical chemistry

Background:

• Accurate description of potential-energy surfaces (PESs) is crucial for understanding chemical reactions.
• Conventional coupled cluster (CC) methods struggle with systems exhibiting strong static correlation, such as bond dissociation.

Purpose of the Study:

• To develop a novel computational method that accurately describes potential-energy surfaces (PESs), especially for bond-breaking processes.
• To combine the strengths of configuration interaction (CI) and coupled cluster (CC) theories for improved accuracy and efficiency.

Main Methods:

• A tailored coupled cluster (TCC) approach is presented, integrating complete active space CI (CAS-CI) with CC theory.
• Cluster amplitudes from CAS-CI are used to incorporate nondynamic correlation into a single-reference CC framework.
• Dynamic correlation is subsequently included using standard CC procedures.

Main Results:

• The TCC method accurately describes the potential-energy surfaces (PESs) for HF, H2O, and N2 molecules, including single, double, and triple bond-breaking.
• The calculated PESs approach the accuracy of full CI methods at the dissociation limit.
• The computational overhead of TCC is negligible compared to standard CC calculations.

Conclusions:

• The TCC method provides a highly accurate and computationally efficient approach for describing molecular potential-energy surfaces.
• This method effectively handles systems with significant nondynamic correlation, such as bond dissociation processes.
• TCC is anticipated to be a generally applicable and valuable tool for various computational chemistry problems.