Joint ICTP/SISSA CM Colloquium

[Cond.Matt. & Stat.Mech.Section]

JOINT ICTP/SISSA    COLLOQUIUM

 ON CONDENSED MATTER PHYSICS

 


Wednesday, 15 May -  4:00 p.m.


 

Luigi Stasi Seminar Room, ICTP Leonardo Building (1st floor)

 


Roberto CAR   ( Princeton University )

 

"Correlated electron calculations with polynomial scaling"

 

Abstract


Due to its simplicity and numerical efficiency, density functional theory (DFT) is the most popular approach for calculating the electronic structure of large molecules and materials. Nevertheless, the accuracy of DFT is not always satisfactory and the search for improved approximations that avoid self-interaction and capture strong electron correlations faces severe difficulties. In this talk I will present an alternative approach in which the one- and two-particle density matrices needed to compute the ground-state energy, are explicit functionals of the natural spin orbital states and their joint occupation probabilities. The scheme is parameter-free and not affected by self-interaction error. In its simplest formulation, restricted to the seniority zero sector of the many-particle Hilbert space, it has the same scaling of Hartree-Fock theory. Yet, it describes strong correlations as demonstrated by calculating the dissociation energy curves of diatomic molecules and linear chains of hydrogen atoms. Improved approximations that retain polynomial cost but are not limited to seniority zero will be also discussed.