Recent advances in reduced density matrix functional theory (RDMFT) and linear response
time-dependent reduced density matrix functional theory (TD-RDMFT) are reviewed. In …

In recent years, Natural Orbital Functional (NOF) theory has gained increasing significance
in quantum chemistry, successfully addressing one of the field's most challenging problems …

λ Δ, Π matrix is described herein, and used to reconstruct the two-particle reduced density
matrix (2-RDM). Then, we have derived a natural orbital functional, the Piris Natural Orbital …

Reduced density matrix functional theory (RDMFT), a promising direction in the problem of
describing strongly correlated systems, is currently limited by its explicit dependence on …

The cumulant expansion gives rise to an useful decomposition of the two‐matrix in which the
pair correlated matrix (cumulant) is disconnected from the antisymmetric product of the one …

The natural orbital functional (NOF) theory is briefly reviewed. The meaning of the top‐down
and bottom‐up approaches for the construction of a NOF is analyzed. A particular …

The one-particle reduced density-matrix (1-RDM) functional theory is a promising alternative
to density-functional theory (DFT) that uses the 1-RDM rather than the electronic density as a …

A recently proposed series of corrections to the earliest J K-only functionals has
considerably improved the prospects of density matrix functional theory (DMFT). Still, the …

A challenging task in natural orbital functional theory is to find an efficient procedure for
doing orbital optimization. Procedures based on diagonalization techniques have confirmed …

This chapter provides a comprehensive review of fundamental concepts related to
approximate natural orbital functionals (NOFs), emphasizing their significance in quantum …