Relativistic CASPT2/RASPT2 Program along with DIRAC Software

Area of Science:

• Nuclear science
• Theoretical chemistry
• Computational physics

Background:

• Exploring electronic states in actinide compounds is crucial but challenging due to relativistic effects and electron correlation.
• Traditional methods like CASSCF have limitations for complex actinide systems.

Purpose of the Study:

• To develop advanced computational tools for accurate theoretical calculations of actinide electronic states.
• To improve the treatment of relativistic effects and electron correlation in these calculations.

Main Methods:

• Developed CASPT2/RASPT2 and DIRAC programs for multiconfigurational perturbation theory with relativistic Hamiltonians.
• Utilized an improved virtual orbital (IVO) approach and CASCI methodologies as reference functions.
• Implemented RASCI-RASPT2 for larger active spaces and parallelized the entire program.

Main Results:

• Demonstrated efficient parallelization of CASCI-CASPT2 on UO2^2+ using 1-256 cores.
• Computed vertical excitation energies of UO2^2+ using RASCI-RASPT2, showing consistency with previous studies.
• Developed a GUI to aid in the selection of orbital spaces for CASPT2/RASPT2 calculations.

Conclusions:

• The developed programs offer efficient and accessible tools for actinide electronic structure calculations.
• Widespread use of these freely available resources is expected to drive further advancements in actinide chemistry.
• The study highlights the successful application of advanced computational methods to complex nuclear science problems.