A road to a multiconfigurational ensemble density functional theory without ghost interactions

Ensemble density functional theory (DFT) is a theory potentially able to describe electronic states inaccessible to traditional time-dependent DFT approaches, e.g. Rydberg and double excitations. When combined with ensemble wavefunction approaches through a range-separation scheme of Stoll and Savin (Density Functional Methods in Physics, 1985, 177-207), a resulting multiconfiguration ensemble DFT is able to address also such challenging phenomena as bond breaking in the electronically excited molecules. Ensemble DFT is, however, crippled by the so-called “ghost interaction” error, analogous to the self-interaction error in the ground-state DFT. We are exploring ways to alleviate this effect. We also study the importance of spin polarization in the density functional, the self-consistency effects and the impact of tunable parameters on the quality of shapes of potential energy surfaces. © 2016 Wiley Periodicals, Inc.