Transition-potential coupled cluster.

Area of Science:

• Computational chemistry
• Quantum chemistry
• Spectroscopy

Background:

• Orbital relaxation is a significant challenge in computational core-hole spectroscopies.
• Linear response methods, such as equation-of-motion coupled cluster with singles and doubles (EOM-CCSD), are particularly affected.
• Existing approaches often rely on increased electron correlation, which can be computationally expensive.

Purpose of the Study:

• To develop a novel computational method that explicitly addresses orbital relaxation in core-hole spectroscopies.
• To introduce a family of transition-potential coupled cluster (TP-CC) methods.
• To assess the accuracy and efficiency of TP-CC methods for calculating core-hole spectra.

Main Methods:

• Proposed an explicit treatment of orbital relaxation using "transition potential" reference orbitals.
• Developed the transition-potential coupled cluster (TP-CC) methodology.
• Introduced and tested the TP-CCSD(12) method, a specific implementation within the TP-CC family.

Main Results:

• The TP-CC methods, particularly TP-CCSD(12), effectively eliminate orbital relaxation errors in core-hole spectra.
• TP-CCSD(12) achieves accuracy comparable to EOM-CCSD for valence electronic structure calculations.
• Accurate computation of x-ray absorption spectra for molecules with first-row atoms is possible at a cost similar to EOM-CCSD.

Conclusions:

• The transition-potential coupled cluster (TP-CC) approach offers a robust solution to the orbital relaxation problem in core-hole spectroscopy.
• TP-CCSD(12) provides a computationally efficient and accurate method for calculating core-hole spectra.
• This work paves the way for more reliable and accessible computational studies of core-hole spectroscopies.