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Palestra – Prof. Mario Piris

Dando continuidade ao Programa de Seminários do Departamento de Física – 2018, promovido pelo PPG-Física, convidamos para o  seminário:

TítuloA global method for the electron correlation

Palestrante: Prof. Mario Piris

University of the Basque Country – Faculty of Chemistry – Polymer Science and Technology Department

Data: 11/12/2018 – terça-feira
Horário: 16:00 h
Local: S401 – Prédio de aulas ICE



The energy of an electron system can be determined exactly from the knowledge of the one- and two-particle reduced density matrices (1- and 2-RDMs). In practical applications, we employ this exact energy functional but using an approximate 2-RDM that is built from the 1-RDM. Approximating the energy functional has important consequences: the theorems obtained for the exact functional of the 1-RDM [1] are no longer valid. As a consequence, the functional N-representability problem arises, that is, we have to comply the requirement that reconstructed 2-RDM must satisfy N-representability conditions to ensure a physical value of the approximate ground-state energy. In the first part of this talk, the role of the N-representability in approximate one-particle functional theories [2] will be analyzed.

The 1-RDM functional is called Natural Orbital Functional (NOF) [3] when it is based upon the spectral expansion of the 1-RDM. Appropriate forms of the two-particle cumulant have led to different implementations [4], being the most recent an interacting-pair model called PNOF7 [5]. The latter is able to treat properly the static (non-dynamic) correlation and recover an important part of dynamic correlation. However, accurate solutions require a balanced treatment of both types of correlation. In the second part of the talk, a new method capable of achieving dynamic and static correlation even in those difficult cases in which both types of correlation are equally important, will be presented.


1. T. L. Gilbert, Phys. Rev. B 12, 2111 (1975); M. Levy, Proc. Natl. Acad. Sci. USA 76, 6062(1979); S. M. Valone, J. Chem. Phys. 73, 1344 (1980).

2. M. Piris, in Many-body approaches at different scales: a tribute to N. H. March on the occasion of his 90th birthday, Chap. 22, pp. 231-247 . New York: Springer (2017).

3. M. Piris, Adv. Chem. Phys. 134, 387–427 (2007).

4. M. Piris, J. M. Ugalde, Int. J. Quantum Chem. 114, 1169–1175 (2014).

5. M. Piris, Phys. Rev. Lett. 119, 063002 (2017); Phys. Rev. A 98, 022504 (2018).