Natural orbital functional for spin-polarized periodic systems

Area of Science:

• Quantum Chemistry
• Computational Physics

Background:

• Natural orbital functional theory (NOFT) is crucial for understanding electron behavior in molecules.
• Existing NOFT methods struggle with systems containing unpaired electrons, limiting their applicability.
• Piris natural orbital functional (PNOF) offers a promising framework for electron correlation.

Purpose of the Study:

• To extend Piris natural orbital functional (PNOF) theory for systems with unpaired electrons.
• To develop accurate models for spin-uncompensated systems using electron pairing approaches.
• To investigate the capability of the extended NOFT in describing strong electron correlation.

Main Methods:

• Extension of PNOF5 (independent pair model) and PNOF7 (interactive pair model) to handle spin-uncompensated systems.
• Inclusion of an explicit form for the two-electron cumulant in high-spin cases.
• Reconstruction of the two-particle reduced density matrix ensuring N-representability and spin conservation.

Main Results:

• The developed theory successfully describes systems with one or more unpaired electrons.
• The extended PNOF models accurately capture strong non-dynamic (static) electron correlation.
• PNOF7 demonstrated excellent agreement with exact diagonalization for hydrogen rings.

Conclusions:

• The presented extension of NOFT provides a robust method for studying spin-uncompensated systems.
• The new models offer a correct description of strong-correlation effects, crucial for various chemical phenomena.
• This work advances the application of NOFT in quantum chemistry and condensed matter physics.