Complete Active Space Self-Consistent Field with GPU-Accelerated Density Fitting.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Photochemistry

Background:

• The complete active space self-consistent field (CASSCF) method is crucial for modeling photochemical reactions.
• Computational expense of four-center two-electron repulsion integrals (ERIs) limits CASSCF in ab initio molecular dynamics.
• Need for efficient methods to accelerate multireference calculations on modern hardware.

Purpose of the Study:

• To implement an atomic orbital (AO)-based GPU-accelerated density fitting (DF) approximation for CASSCF.
• To reduce the computational cost of CASSCF calculations in ab initio molecular dynamics.
• To enable high-throughput, high-accuracy multireference simulations on GPU architectures.

Main Methods:

• Implementation of AO-based GPU-accelerated DF approximation for CASSCF within the TeraChem software.
• Validation using salicylaldimine to assess accuracy of relative and excitation energies.
• Ab initio multiple spawning dynamics simulations of excited-state intramolecular proton transfer (ESIPT).

Main Results:

• The DF approximation introduces negligible errors in relative energies (<10 microHartrees for excitation energies).
• DF-CASSCF achieves significant speedups (>10x) for total energy and gradient calculations.
• DF-CASSCF simulations of ESIPT reduce wall time by 3-30x compared to integral-direct methods.

Conclusions:

• GPU-accelerated DF-CASSCF provides a computationally efficient and accurate approach for multireference simulations.
• This method significantly lowers the barrier for complex photochemical process modeling.
• Enables practical application of high-accuracy ab initio molecular dynamics on modern GPU hardware.