A state interaction spin-orbit coupling density matrix renormalization group method.

Area of Science:

• Quantum Chemistry
• Computational Physics
• Electronic Structure Theory

Background:

• Accurate calculation of spin-orbit coupling (SOC) is crucial for understanding electronic properties of atoms and molecules.
• Existing methods may face challenges with computational cost or accuracy for complex systems.
• Density matrix renormalization group (DMRG) is a powerful tool for strongly correlated systems.

Purpose of the Study:

• To develop and implement a novel State Interaction Spin-Orbit (SISO) coupling method.
• To integrate DMRG wavefunctions with the spin-orbit mean-field (SOMF) operator for enhanced accuracy.
• To benchmark the DMRG-SISO scheme against established methods for atomic and molecular systems.

Main Methods:

• Implementation of a spin-adapted algorithm for computing transition density matrices between matrix product states.
• Application of the DMRG-SISO scheme to calculate zero-field splitting (ZFS) in copper and gold atoms.
• Computation of SOC effects on the spin-ladder states of an iron-sulfur dimer complex.

Main Results:

• Accurate benchmark calculations for the zero-field splitting of copper and gold atoms were performed.
• Comparison with complete active space self-consistent-field (CASSCF) and second-order complete active space perturbation theory (CASPT2) showed good agreement.
• The study determined the splitting of the lowest quartet and sextet states for the iron-sulfur dimer complex.

Conclusions:

• The developed DMRG-SISO scheme provides accurate results for spin-orbit coupling effects.
• The method shows significant potential for studying electronic structures of complex molecular systems.
• The magnitude of ZFS for higher states in the iron-sulfur dimer approaches a substantial fraction of the Heisenberg exchange parameter.