  A $2\times2\times2$ charge density wave (CDW) was recently observed deep
inside the antiferromagnetic phase of a Kagome metal FeGe. A key question is
whether the CDW in FeGe is driven by its electronic correlation and magnetism.
Here, we address this problem using density functional theory and its
combination with $U$ as well as dynamical mean-field theory. Our calculations
show that large dimerization ($\sim 1.3 \overset{\lower.5em\circ}{\mathrm{A}}$)
of Ge1-sites along $c$-axis will enhance electronic correlation of the Fe-$3d$
orbitals and, as a result, it enhances the spin-polarization and saves more
magnetic exchange energies. We find that the balance between magnetic energy
saving and structural energy cost via partially dimerizing Ge1-sites in an
enlarged superstructure, could induce a new local minimum in total energies.
The response to the large partial Ge1-dimerization will induce additional small
modulations ($<0.05 \overset{\lower.5em\circ}{\mathrm{A}}$) of other sites in
the Kagome and honeycomb layers, which further reduces the total energy and
leads to a stable $2\times 2\times 2$ CDW ground state in FeGe. Our results are
in good agreement with the existing experiments and reveal a novel CDW
mechanism driven by the interplay of structure, electronic correlation and
magnetism.
