Abundant Lattice Instability in Kagome Metal ScV₆Sn₆

Kagome materials are emerging platforms for studying charge and spin orders. In this Letter, we have revealed a rich lattice instability in a Z₂ kagome metal ScV₆Sn₆ by first-principles calculations. Beyond verifying the √3×√3×3 charge density wave (CDW) order observed by the recent experiment, we further identified three more possible CDW structures, i.e., √3×√3×2 CDW with P6/mmm symmetry, 2×2×2 CDW with Immm symmetry, and 2×2×2 CDW with P6/mmm symmetry. The former two are more energetically favored than the √3×√3×3 phase, while the third one is comparable in energy. These CDW distortions involve mainly out-of-plane motions of Sc and Sn atoms, while V atoms constituting the kagome net are almost unchanged. We attribute the lattice instability to the smallness of Sc atomic radius. In contrast, such instability disappears in its sister compounds RV₆Sn₆ (R is Y, or a rare-earth element), which exhibit quite similar electronic band structures to the Sc compound, because R has a larger atomic radius. Our work indicates that ScV₆Sn₆ might exhibit varied CDW phases in different experimental conditions and provides insights to explore rich charge orders in kagome materials.