A systematic construction of configuration interaction wavefunctions in the complete CI space

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Electronic Structure Theory

Background:

• Configuration Interaction (CI) methods are crucial for accurate electronic structure calculations.
• Monte Carlo Configuration Interaction (MCCI) offers a computationally efficient alternative to full CI.
• Exploring and systematically constructing CI wavefunctions remains an active area of research.

Purpose of the Study:

• To introduce and evaluate a systematic variant of the MCCI method.
• To compare the performance of systematic-MCCI against standard MCCI and pruned-FCI approaches.
• To assess the scalability and accuracy of systematic-MCCI for various molecular systems.

Main Methods:

• Development of systematic-MCCI by batch-wise consideration of the interacting space.
• Comparison with MCCI and pruned-Full Configuration Interaction (FCI) methods.
• Application to neon atom, water dissociation, carbon monoxide excited state, and chromium dimer.

Main Results:

• Systematic-MCCI, MCCI, and pruned-MCCI show comparable accuracy for neon's ground state, recovering ~99% of correlation energy.
• MCCI performs comparably to systematic approaches for water dissociation potential energy surface.
• Systematic-MCCI demonstrates good scalability despite longer run times and avoids local minima encountered by MCCI in the chromium dimer case.

Conclusions:

• Systematic-MCCI provides a robust and accurate approach for constructing CI wavefunctions.
• The method shows comparable performance to existing MCCI techniques while offering systematic exploration.
• Scalability is good, and the approach can avoid pitfalls like local minima in complex systems.