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 aforementioned soft modes, we found that the stable structure has the Immm symmetry and can be achieved by shifts of Ge atoms. The occurrence of two soft modes induces the first-order phase transition, which leads to the CDW order. Additionally, we show that the final structure realizes a distorted honeycomb Ge lattice, as well as a nonflat 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.

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• Charge density waves
• Phonons
• Ab initio calculations
• Band structure methods
• DFT+U