Treating molecules in arbitrary spin states using the parametric two-electron reduced-density-matrix method.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Electronic Structure Theory

Background:

• Parametric variational 2-RDM methods minimize electronic energy using parameterized 2-RDMs.
• The M 2-RDM parametrization offers a computationally efficient approach to electronic structure calculations.

Purpose of the Study:

• Extend the M parametric 2-RDM method to handle molecules in arbitrary spin states.
• Evaluate the accuracy and efficiency of the extended method for describing molecular properties.

Main Methods:

• Utilized approximate N-representability conditions to derive the M parametric 2-RDM method for arbitrary spin states.
• Compared results with the K parametric 2-RDM method and various wavefunction methods.

Main Results:

• The M method accurately describes bond breaking in open-shell molecules (e.g., triplet B2, OH+) even with strong correlation.
• Achieved higher correlation energy capture than coupled cluster with single and double excitations (CCSD) at a lower computational cost.
• Computed 2-RDMs demonstrated near N-representability across different geometries.

Conclusions:

• The extended M parametric 2-RDM method provides a robust and efficient tool for studying molecules in diverse spin states.
• This approach offers a promising alternative for electronic structure calculations, particularly for systems with strong electron correlation.