Open-Shell Tensor Hypercontraction.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Wavefunction-based quantum-chemical methods like Møller-Plesset perturbation theory (MPn) face computational cost scaling challenges with increasing molecular size.
• Least-squares tensor hypercontraction (LS-THC) offers efficient factorization of the two-electron integral tensor, reducing computational complexity.
• Open-shell systems (ions, radicals) are crucial in chemistry but computationally demanding to study with traditional methods.

Purpose of the Study:

• To extend least-squares tensor hypercontracted (LS-THC) second- and third-order Møller-Plesset perturbation theory (MP2 and MP3) to open-shell molecular systems.
• To investigate the accuracy and efficiency of these extended methods for open-shell electronic structure calculations.
• To provide a computationally tractable approach for studying reactive chemical species.

Main Methods:

• Development of open-shell variants of LS-THC-MP2 and LS-THC-MP3 using diagrammatic techniques.
• Application of explicit spin summation to incorporate open-shell characteristics.
• Benchmarking the LS-THC-MPn methods on various test systems, including alkanes, bond-breaking scenarios, and radical stabilization.

Main Results:

• The developed open-shell LS-THC-MPn methods demonstrate accuracy comparable to their closed-shell counterparts.
• The computational cost scaling is significantly reduced due to the LS-THC factorization.
• The methods show robustness, being insensitive to specific chemical interactions, geometries, or moderate spin contamination.

Conclusions:

• The extension of LS-THC-MPn to open-shell systems is a significant advancement in computational quantum chemistry.
• These methods provide a reliable and efficient tool for studying a wide range of open-shell molecular systems.
• LS-THC-MPn offers a promising avenue for reducing computational burdens in theoretical chemistry research.