  Electron-correlation-driven phonon soft modes have been recently reported in
the antiferromagnetic kagome FeGe compound and associated with the observed
charge density wave (CDW). In this paper, we present a systematic investigation
of the CDW origin in the context of the ab initio lattice dynamics study.
Performing the group theory analysis of the mentioned soft mode, we found that
the stable structure has the Immm symmetry and can be achieved by shifts of Ge
atoms. Additionally, we show that the final structure realizes a distorted
honeycomb Ge lattice as well as a non-flat kagome-like Fe net. For
completeness, we present the electronic properties calculations. From the
theoretical STM topography simulation, we indicate that the observed CDW occurs
in the deformed honeycomb Ge sublattice.
