A natural linear scaling coupled-cluster method

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Coupled-cluster methods are accurate for electronic structure but computationally expensive for large systems.
• Scaling limitations hinder the application of high-accuracy methods to extended molecular structures.

Purpose of the Study:

• To develop a linear scaling coupled-cluster (NLSCC) method for efficient calculation of electronic correlation energies in large systems.
• To demonstrate the transferability of local correlation energies using a localized molecular orbital (LMO) basis.

Main Methods:

• Implementation of a natural linear scaling coupled-cluster (NLSCC) approach using a localized molecular orbital (LMO) basis.
• Calculation of coupled-cluster singles and doubles (CCSD) wave functions and energies on small system subunits.
• Summation of local occupied orbital correlation energies from subunits to obtain total correlation energy for extended systems.

Main Results:

• The NLSCC method achieves natural linear scaling for electronic correlation energy calculations.
• Demonstrated accuracy by comparing results for polyglycine molecules with large-scale LCCSD calculations.
• Successfully applied to alkane and polyglycine systems, showing the method's applicability to nonperiodic extended systems.

Conclusions:

• The NLSCC method provides an efficient and accurate way to compute correlation energies for very large molecular systems.
• The use of LMOs and local correlation energies enables linear scaling, overcoming limitations of traditional CCSD methods.
• This approach allows for the treatment of extended systems with effectively infinite basis set sizes.