Automatic active space selection for the similarity transformed equations of motion coupled cluster method

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• The similarity transformed equations of motion (STEOM) coupled cluster method is a powerful tool for calculating excited states.
• Selecting an appropriate active space is crucial for the accuracy and efficiency of STEOM calculations.
• Manual active space selection can be time-consuming and requires significant expertise.

Purpose of the Study:

• To develop an efficient and automatic scheme for active space selection in STEOM coupled cluster calculations.
• To enable the use of STEOM as a "black box" method, reducing the need for manual intervention.
• To validate the performance of the proposed scheme across various types of excited states.

Main Methods:

• The proposed scheme utilizes state-averaged configuration interaction singles (CIS) natural orbitals for active space selection.
• This approach integrates seamlessly with the STEOM coupled cluster method.
• The method is designed for automated implementation, minimizing user input.

Main Results:

• The automatic active space selection scheme demonstrates efficiency and accuracy.
• The performance of the scheme was evaluated for singlet and triplet valence excited states.
• The scheme was also tested on challenging charge transfer and Rydberg excited states, showing reliable results.

Conclusions:

• The developed scheme provides an effective automated solution for active space selection in STEOM.
• This advancement makes complex excited state calculations more accessible and user-friendly.
• The method shows broad applicability for various excited electronic states in computational chemistry.