An atomic orbital-based formulation of analytical gradients and nonadiabatic coupling vector elements for the...

Area of Science:

• Quantum chemistry
• Computational chemistry
• Theoretical chemistry

Background:

• State-averaged complete active space self-consistent field (SA-CASSCF) methods are crucial for studying electronic states of molecules.
• Previous algorithms for SA-CASSCF orbital optimization had limitations in computational scaling with molecular size.

Purpose of the Study:

• To extend existing SA-CASSCF algorithms for efficient calculation of analytic gradients and nonadiabatic coupling vectors.
• To enable routine geometry optimizations and nonadiabatic dynamics simulations for large molecular systems.

Main Methods:

• Developed algorithms for analytic gradient and nonadiabatic coupling vector calculations within the SA-CASSCF framework.
• Leveraged sparsity in the atomic orbital basis set to reduce computational scaling.
• Utilized graphical processing units (GPUs) for accelerated computations.

Main Results:

• Achieved significantly reduced computational scaling for SA-CASSCF calculations.
• Successfully performed SA-CASSCF geometry optimizations for molecules exceeding 1000 atoms.
• Demonstrated the potential for routine minimal energy conical intersection searches and nonadiabatic dynamics for systems with hundreds of atoms.

Conclusions:

• The enhanced SA-CASSCF algorithms provide a computationally efficient approach for large molecular systems.
• This work paves the way for routine investigations of complex nonadiabatic processes in large molecules.
• The developed methods will accelerate research in areas like photochemistry and reaction dynamics.