Two-component multi-configurational second-order perturbation theory with Kramers restricted complete active space...

Area of Science:

• Quantum Chemistry
• Relativistic Effects
• Computational Spectroscopy

Background:

• Accurate prediction of atomic properties for heavy elements is crucial in chemistry and physics.
• Existing methods struggle with relativistic effects and electron correlation in heavy systems.
• Kramers restricted complete active space self-consistent field (KRCASSCF) provides a foundation but requires further refinement.

Purpose of the Study:

• To develop and implement a novel relativistic multi-configurational perturbation theory method.
• To improve the accuracy of calculations for ionization potentials and excitation energies.
• To accurately compute atomic properties of superheavy elements.

Main Methods:

• Formulation and implementation of KRCASPT2, a two-component multi-configurational second-order perturbation theory.
• Utilizing a Kramers restricted complete active space self-consistent field (KRCASSCF) reference function.
• Incorporating spin-orbit relativistic effective core potential and a generalized two-component Fock matrix.

Main Results:

• KRCASPT2 shows significant improvement over KRCASSCF for 6p-block elements.
• Calculated ionization potentials and excitation energies show closer agreement with experimental data.
• Accurate atomic properties for 7p-block superheavy elements are presented, with comparisons to lighter homologues.

Conclusions:

• KRCASPT2 offers a more accurate and robust approach for relativistic electronic structure calculations.
• The method successfully treats degenerate states by maintaining Kramers symmetry.
• This work paves the way for more precise predictions of properties for heavy and superheavy elements.