TY  - JOUR
PB  - SciPost Foundation
DO  - 10.21468/SciPostPhys.14.5.120
TI  - Deriving density-matrix functionals for excited states
PY  - 2023/05/19
UR  - https://www.scipost.org/SciPostPhys.14.5.120
JF  - SciPost Physics
JA  - SciPost Phys.
VL  - 14
IS  - 5
SP  - 120
A1  - Liebert, Julia
AU  - Schilling, Christian
AB  - We initiate the recently proposed $w$-ensemble one-particle reduced density matrix functional theory ($w$-RDMFT) by deriving the first functional approximations and illustrate how excitation energies can be calculated in practice. For this endeavour, we first study the symmetric Hubbard dimer, constituting the building block of the Hubbard model, for which we execute the Levy-Lieb constrained search. Second, due to the particular suitability of $w$-RDMFT for describing Bose-Einstein condensates, we demonstrate three conceptually different approaches for deriving the universal functional in a homogeneous Bose gas for arbitrary pair interaction in the Bogoliubov regime. Remarkably, in both systems the gradient of the functional is found to diverge repulsively at the boundary of the functional's domain, extending the recently discovered Bose-Einstein condensation force to excited states. Our findings highlight the physical relevance of the generalized exclusion principle for fermionic and bosonic mixed states and the curse of universality in functional theories.
ER  -

@Article{10.21468/SciPostPhys.14.5.120,
	title={{Deriving density-matrix functionals for excited states}},
	author={Julia Liebert and Christian Schilling},
	journal={SciPost Phys.},
	volume={14},
	pages={120},
	year={2023},
	publisher={SciPost},
	doi={10.21468/SciPostPhys.14.5.120},
	url={https://scipost.org/10.21468/SciPostPhys.14.5.120},
}