Single-Reference Methods Based on Complex Orbital in Electronic Structure Calculations for High-Symmetry Systems.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Electronic Structure Theory

Background:

• Multireference (MR) states in electronic structure calculations typically require complex multideterminant wave functions using real molecular orbitals (MOs).
• Certain specific MR states in atoms and molecules can be simplified using complex MOs, allowing for single-determinant representations.

Purpose of the Study:

• To investigate the utility of complex molecular orbitals (MOs) for representing multireference (MR) states in electronic structure calculations.
• To assess the performance of various computational methods employing complex MOs for specific atomic and molecular systems.

Main Methods:

• Utilized complex MOs to represent specific MR states in atoms, linear molecules, and nonlinear molecules with real two-dimensional irreducible representations.
• Employed angular momentum symmetry-broken methods within density functional theory (DFT) for selected MR states.
• Assessed the performance of MP2, CCSD, CCSD(T), and DFT methods with complex MOs.

Main Results:

• Complex MOs enable single-determinant representation for certain MR states, particularly those with angular momentum symmetry.
• CCSD(T) calculations with complex MOs demonstrated high accuracy for applicable cases.
• DFT calculations provided reasonable accuracy, dependent on the chosen exchange-correlation functionals.

Conclusions:

• Complex MOs offer an efficient alternative for describing specific multireference states in quantum chemistry.
• The use of complex MOs in conjunction with methods like CCSD(T) and DFT can lead to accurate and computationally feasible electronic structure calculations.