Complete active space configuration interaction from state-averaged configuration interaction singles natural...

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Photochemistry

Background:

• A novel complete active space configuration interaction (CASCI) method, CISNO-CASCI, utilizes state-averaged natural orbitals.
• This method demonstrates comparable or superior performance to state-averaged complete active space self-consistent field (SA-CASSCF) for various molecular systems.
• Development has been hindered by the absence of analytic first derivatives and derivative couplings for CISNO-CASCI.

Purpose of the Study:

• To develop and implement analytic first derivatives and derivative couplings for the CISNO-CASCI method.
• To accelerate the computation of these derivatives using graphical processing units (GPUs).
• To assess the practicality of the enhanced CISNO-CASCI method for large-scale photochemical simulations.

Main Methods:

• A Lagrangian-based formulation was employed to derive the analytic first derivatives of the CISNO-CASCI energy.
• An efficient computational implementation of the derived equations was developed.
• The implementation was accelerated using graphical processing units (GPUs).

Main Results:

• Analytic first derivatives and derivative couplings for CISNO-CASCI were successfully formulated and implemented.
• The GPU acceleration significantly enhanced computational efficiency.
• The study demonstrated the method's capability for simulating photochemical processes.

Conclusions:

• The developed analytic derivatives and GPU implementation make CISNO-CASCI practical for dynamical simulations.
• The method is suitable for studying photochemical processes in large molecular systems (hundreds of atoms).
• This advancement opens new avenues for theoretical investigations in photochemistry.