QUEST#4X: An Extension of QUEST#4 for Benchmarking Multireference Wave Function Methods.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Existing datasets primarily assess single-reference methods for closed-shell systems.
• A comprehensive dataset for multireference methods on open-shell excited states is needed.
• Open-shell systems are crucial for understanding various chemical phenomena.

Purpose of the Study:

• Introduce QUEST#4X, an extended dataset for evaluating multireference methods.
• Assess the performance of static-dynamic-static configuration interaction (SDSCI) and static-dynamic-static second-order perturbation theory (SDSPT2).
• Provide benchmarks for low-lying excited states of open-shell systems.

Main Methods:

• Developed the QUEST#4X dataset, extending QUEST#4 for open-shell systems.
• Utilized iterative configuration interaction with selection and second-order perturbation correction (iCIPT2) for near-exact benchmarks.
• Calibrated SDSCI and SDSPT2 against iCIPT2 results.

Main Results:

• SDSCI demonstrates accuracy comparable to internally contracted multireference configuration interaction with singles and doubles (ic-MRCISD) at lower computational cost.
• SDSPT2 exhibits performance similar to multistate n-electron valence second-order perturbation theory (MS-NEVPT2).
• SDSPT2 offers a unified approach for single and multiple state calculations.

Conclusions:

• SDSCI and SDSPT2 are validated as accurate and efficient methods for open-shell excited states.
• The QUEST#4X dataset provides a robust platform for future method development.
• These findings establish a strong foundation for the application of SDSCI and SDSPT2.