Multireference Fock Space Coupled-Cluster Method for the (3,0) Sector.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• The multireference coupled cluster (MRCC) theory is a powerful quantum chemical method for describing electron correlation in molecules.
• Previous Fock space MRCC formulations were limited to specific electron number sectors, restricting their applicability.
• Treating systems with three valence electrons requires extending these theoretical frameworks.

Purpose of the Study:

• To implement and apply a novel Fock space multireference coupled cluster (FS-MRCC) theory in the (3,0) sector.
• To enable accurate electronic structure calculations for molecules with three valence electrons.
• To compute potential energy curves and spectroscopic constants for specific diatomic molecules.

Main Methods:

• Implementation of the Fock space multireference coupled cluster (FS-MRCC) theory in the (3,0) sector.
• Utilizing a triply ionized species as the reference state for neutral molecule calculations.
• Application of the restricted Hartree-Fock scheme for closed-shell reference states and fragments.
• Calculation of potential energy curves and spectroscopic constants.

Main Results:

• Successful extension of FS-MRCC theory to the (3,0) sector, accommodating systems with three valence electrons.
• Accurate calculation of potential energy curves for LiBe, LiC, and NaC molecules.
• Determination of spectroscopic constants for the studied diatomic molecules.

Conclusions:

• The (3,0) FS-MRCC sector provides a robust theoretical tool for studying molecules with three valence electrons.
• The method is particularly suitable for alkali metal and alkaline earth metal diatomics and related compounds.
• The calculated spectroscopic data for LiBe, LiC, and NaC are valuable for future experimental and theoretical investigations.