A configuration-based heatbath-CI for spin-adapted multireference electronic structure calculations with large active...

Area of Science:

• Quantum Chemistry
• Computational Physics

Background:

• Accurate electronic structure calculations are crucial for understanding molecular properties.
• Existing methods face challenges with computational cost and accuracy for large systems.

Purpose of the Study:

• To develop a spin-pure configuration-based implementation of the Heatbath Configuration Interaction (HCI) algorithm.
• To improve the efficiency and accuracy of selective configuration interaction methods.

Main Methods:

• Implemented a spin-pure configuration-based approach for HCI.
• Utilized strict pruning of the configurational space for compact wavefunctions.
• Optimized Hamiltonian diagonalization using just-in-time compilation.
• Employed a tree-based representation for efficient 2-electron connection searches.
• Applied prefix-based parallelization and batching for PT2-correction calculations.

Main Results:

• Achieved a compact wavefunction representation through optimized configurational space pruning.
• Minimized redundant matrix-matrix multiplications for enhanced performance.
• Facilitated efficient search for 2-electron connections.
• Reduced memory requirements and improved load balancing in PT2-correction calculations.
• Avoided semistochastic approaches for PT2 corrections even in large configurational spaces.

Conclusions:

• The developed spin-pure HCI method offers high performance and efficiency.
• The approach provides a compact wavefunction representation and avoids computationally expensive semistochastic methods.
• Demonstrated strengths and weaknesses through various test cases, paving the way for advanced quantum chemical studies.