Natural Orbitals: Old Concepts, New Developments
Joint CQT Colloquium with NUS Physics & NUS Chemistry
Speaker: Jerzy Ciosłowski, University of Szczecin
Abstract: Since their introduction in 1955, the natural orbitals (NOs) have been employed in numerous approaches to quantum-mechanical description of systems composed of indistinguishable particles, proving to be an indispensable tool in both computation and interpretation of electronic and nuclear wavefunctions. However, despite their importance to quantum chemistry and nuclear physics, the NOs have been the subject of a relatively small number of studies aiming at understanding of their properties. This disappointing state of affairs has been rectified only very recently with the uncovering of high-order off-diagonal cusp conditions for the reduced density matrices of Coulombic species that opened an avenue to an asymptotic formalism for the NOs. This approach has turned out to reveal surprising universalities among the NOs (and their occupation numbers) of diverse systems. It also produced rigorous estimates for the truncation errors in the electronic properties computed with basis sets of finite sizes employed in quantum-chemical calculations. The present talk reviews both the basic properties of the NOs and those afforded by the aforementioned new developments.
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