Electronically driven anharmonicities in charge-density-wave materials*

Charge-density waves (CDWs) occupy an important position in the phase diagram of low-dimensional systems such as the transition metal dichalcogenide monolayers. Although a CDW can often be identified already from the undistorted structure in linear response, anharmonic effects are eventually responsible for the stabilization of the distorted phase and its precise properties. To study the mechanisms responsible for these anharmonicities, we calculate Born-Oppenheimer potential energy surfaces for lattice distortions in 1T-TaS₂ ( √13 × √13), 1T-VS₂ (7 × √3), and 2H-NbSe₂ (3 × 3), and we establish a connection to the electronic structure of these materials.