Variational minimization scheme for the one-particle reduced density matrix functional theory in the ensemble...

Area of Science:

• Quantum Chemistry
• Computational Materials Science
• Theoretical Physics

Background:

• One-particle reduced density-matrix (1-RDM) functional theory is a promising alternative to density-functional theory (DFT).
• Current limitations include the absence of a Kohn-Sham scheme and complex N-representability conditions, hindering widespread adoption.
• Existing ensemble N-representability conditions, restricted to natural orbitals, lead to functionals that perform poorly across all correlation regimes.

Purpose of the Study:

• To propose a novel variational minimization scheme for 1-RDM functional theory within the ensemble N-representable domain.
• To overcome the limitations of the natural orbital representation for 1-RDM functionals.
• To pave the way for developing functionals of orbital occupations, addressing a key challenge in site-occupation functional theory.

Main Methods:

• Development of a variational minimization scheme for 1-RDM functionals.
• The scheme is not restricted to the natural orbital representation of the 1-RDM.
• Splitting the minimization into diagonal and off-diagonal parts of the 1-RDM.

Main Results:

• The proposed method allows for a variational minimization scheme not confined to natural orbitals.
• The approach facilitates the development of functionals based on orbital occupations.
• Successful testing on the uniform Hubbard model and the dihydrogen molecule using established functionals.

Conclusions:

• The proposed variational minimization scheme expands the applicability of 1-RDM functional theory.
• This work opens new avenues for developing advanced functionals, particularly those targeting orbital occupations.
• The findings contribute to the advancement of electronic structure calculations and functional design in quantum chemistry.