Large-Scale Electron Correlation Calculations: Rank-Reduced Full Configuration Interaction.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Electronic Structure Theory

Background:

• Full Configuration Interaction (FCI) is the gold standard for accurate electronic structure calculations but is computationally intractable for large systems.
• Existing methods struggle with the exponential scaling of the FCI wave function with system size.

Purpose of the Study:

• To introduce and validate the rank-reduced Full Configuration Interaction (RR-FCI) method.
• To demonstrate the accuracy and efficiency of RR-FCI for large quantum systems.

Main Methods:

• Developed a variational approach for calculating large FCI wave functions using rank reduction.
• Implemented GPU-accelerated matrix-vector products for efficient computation.
• Applied RR-FCI to acenes and molecular nitrogen dissociation.

Main Results:

• RR-FCI achieves energies within kcal/mol accuracy of FCI.
• Computational cost scales as the square root of the number of determinants, a significant improvement over linear scaling.
• Enabled calculations with over 2.4 x 10^16 configurations using 30 electrons in 30 orbitals.
• RR-FCI results for acene excitation energies and N2 dissociation agree well with FCI, DMRG, and experimental data.

Conclusions:

• RR-FCI is a computationally efficient and accurate alternative to traditional FCI methods.
• The method shows particular advantages for calculating relative energies.
• RR-FCI significantly expands the feasibility of high-accuracy electronic structure calculations for larger molecular systems.