COLUMBUS─An Efficient and General Program Package for Ground and Excited State Computations Including Spin-Orbit...

Area of Science:

• Quantum chemistry
• Computational physics
• Theoretical chemistry

Background:

• High-level multireference computations are essential for accurately describing complex atomic and molecular systems.
• Existing methods often struggle with open-shells, excited states, and heavy elements influenced by spin-orbit coupling.
• Accurate modeling is crucial for understanding phenomena like ultrafast photochemistry.

Purpose of the Study:

• To present the capabilities and recent developments of the COLUMBUS program system.
• To highlight its application in diverse atomic and molecular systems, including those with heavy elements.
• To showcase advancements in computational methods and their impact on chemical dynamics.

Main Methods:

• Utilizes multireference configuration interaction (MRCI) and multireference averaged quadratic coupled cluster (MR-AQCC) methods.
• Incorporates spin-orbit coupling (SOC) directly within the MRCI step for heavy element systems.
• Employs analytic energy gradients and nonadiabatic couplings for dynamics studies.

Main Results:

• COLUMBUS enables detailed studies of open-shells, excited states, and heavy elements (lanthanides, actinides) due to SOC.
• The system provides insights into ultrafast photochemistry through dynamics studies.
• New developments include spin density computations, improved ionic state descriptions, AQCC enhancements, and GPU porting.

Conclusions:

• COLUMBUS is a versatile tool for high-level multireference computations, particularly for systems with strong spin-orbit coupling.
• Recent advancements enhance its applicability to electronic resonances, molecules in strong laser fields, and complex chemical dynamics.
• The program facilitates a deeper understanding of atomic and molecular properties and processes.