Analytic gradients for relativistic exact-two-component equation-of-motion coupled-cluster singles and doubles method

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Relativistic Quantum Mechanics

Background:

• Relativistic effects are crucial for heavy elements like radium.
• Accurate computational methods are needed to study their electronic structure and properties.
• Equation-of-motion coupled-cluster (EOMCC) methods provide high accuracy for electronic excited states.

Purpose of the Study:

• To implement analytic gradients for the spinor-based relativistic EOMCC singles and doubles (CCSD) method.
• To apply this method to investigate the electronic ground and excited states of radium-containing molecules.
• To explore the role of spin-orbit coupling and identify potential applications of these molecules.

Main Methods:

• Development and implementation of analytic gradients for relativistic EOMCCSD.
• Utilized an exact two-component Hamiltonian with atomic mean-field spin-orbit integrals.
• Performed calculations for equilibrium structures and harmonic vibrational frequencies.

Main Results:

• Successfully computed analytic gradients for the relativistic EOMCCSD method.
• Calculated structural and vibrational properties for radium mono-amide (RaNH2) and radium mono-methoxide (RaOCH3).
• Demonstrated that spin-orbit coupling quenches Jahn-Teller effects in RaOCH3, leading to a C3v structure.
• Identified radium atoms in these molecules as efficient optical cycling centers.

Conclusions:

• The developed method provides accurate gradients for relativistic EOMCCSD calculations.
• Spin-orbit coupling significantly influences the electronic structure and geometry of heavy-element molecules.
• Radium-containing molecules show promise for applications as optical cycling centers.