TY  - JOUR
PB  - SciPost Foundation
DO  - 10.21468/SciPostPhys.17.2.038
TI  - Exact first-order effect of interactions on the ground-state energy of harmonically-confined fermions
PY  - 2024/08/07
UR  - https://scipost.org/SciPostPhys.17.2.038
JF  - SciPost Physics
JA  - SciPost Phys.
VL  - 17
IS  - 2
SP  - 038
A1  - Le Doussal, Pierre
AU  - Smith, Naftali R.
AU  - Argaman, Nathan
AB  - We consider a system of $N$ spinless fermions, interacting with each other via a power-law interaction $\epsilon/r^n$, and trapped in an external harmonic potential $V(r) = r^2/2$, in $d=1,2,3$ dimensions. For any $0 < n < d+2$, we obtain the ground-state energy $E_N$ of the system perturbatively in $\epsilon$, $E_{N}=E_{N}^{(0)}+\epsilon E_{N}^{(1)}+O(\epsilon^{2})$. We calculate $E_{N}^{(1)}$ exactly, assuming that $N$ is such that the "outer shell" is filled. For the case of $n=1$ (corresponding to a Coulomb interaction for $d=3$), we extract the $N \gg 1$ behavior of $E_{N}^{(1)}$, focusing on the corrections to the exchange term with respect to the leading-order term that is predicted from the local density approximation applied to the Thomas-Fermi approximate density distribution. The leading correction contains a logarithmic divergence, and is of particular importance in the context of density functional theory. We also study the effect of the interactions on the fermions' spatial density. Finally, we find that our result for $E_{N}^{(1)}$ significantly simplifies in the case where $n$ is even.
ER  -

@Article{10.21468/SciPostPhys.17.2.038,
	title={{Exact first-order effect of interactions on the ground-state energy of harmonically-confined fermions}},
	author={Pierre Le Doussal and Naftali R. Smith and Nathan Argaman},
	journal={SciPost Phys.},
	volume={17},
	pages={038},
	year={2024},
	publisher={SciPost},
	doi={10.21468/SciPostPhys.17.2.038},
	url={https://scipost.org/10.21468/SciPostPhys.17.2.038},
}