Efficient implementation of restricted active space configuration interaction with the hole and particle...

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Restricted Active Space Configuration Interaction (RASCI) provides a balanced treatment of electronic states.
• Existing RASCI methods have limitations in flexibility and computational efficiency.

Purpose of the Study:

• To present a new, general integral-driven implementation of the RASCI(h,p) method.
• To enhance the flexibility of reference configurations and excitation operators in RASCI calculations.

Main Methods:

• Integral-driven algorithm for RASCI calculations.
• Implementation of hole and particle truncation (RASCI(h,p)).
• Support for arbitrary reference configurations and excitation operators (ionization, electron attachment, spin-flip).

Main Results:

• Demonstrated applicability to water molecule ground state calculations up to the full-CI limit.
• Validated performance for all-trans linear polyenes with variable spin-flip excitations.
• Successfully computed low-lying states of fluorine molecule using a double-ionization potential operator.

Conclusions:

• The new RASCI(h,p) implementation is versatile and computationally efficient.
• The method accurately describes ground and excited states across various molecular systems.
• This work advances quantum chemical modeling capabilities.