State Interaction for Relativistic Four-Component Methods: Choose the Right Zeroth-Order Hamiltonian for Late-Row...

Area of Science:

• Quantum Chemistry
• Relativistic Quantum Mechanics
• Computational Chemistry

Background:

• Relativistic effects are crucial for accurately describing heavy elements.
• State interaction methods traditionally use simplified scalar-relativistic Hamiltonians.
• Accurate treatment of electron correlation and relativistic effects is computationally demanding.

Purpose of the Study:

• To develop and investigate novel perturbative schemes for relativistic four-component Hamiltonians.
• To improve the accuracy of state interaction methods by augmenting the zeroth-order Hamiltonian.
• To establish a theoretical foundation for low-scaling, high-accuracy relativistic calculations.

Main Methods:

• Spin-separation of the Dirac-Coulomb-Breit Hamiltonian.
• Development of augmented zeroth-order Hamiltonians with increasing accuracy.
• Benchmarking against ground-state fine-structure splitting in late-row atoms and diatomic hydrides.

Main Results:

• Augmenting the zeroth-order Hamiltonian with vector-relativistic operators significantly improves accuracy.
• Scalar-relativistic approximations lead to substantial errors in fine-structure splitting.
• The proposed schemes show convergence towards the variational limit.

Conclusions:

• Augmented zeroth-order Hamiltonians offer a pathway to high-accuracy relativistic calculations.
• The developed methods are suitable for describing late-row elements where relativistic effects dominate.
• This work provides a theoretical basis for future efficient relativistic quantum chemistry methods.