DFT Methods. The three DSG cells used for this work were: u24C, 1c24C, and 2c24C, which were first geometrically optimized using DFT. The Vienna ab initio simulation package (VASP) was used to run all DFT calculations. The pseudopotentials were constructed using the projector augmented wave (PAW) formalism. We set the plane-wave cutoff to 520 eV for our DSG systems. The total energy was calculated within the Perdew-Burke-Ernzerhof (PBE) form of the generalized gradient approximation (GGA) exchange-correlation functional. Brillouin zone sampling was performed using a Monkhorst-Pack k-point grid size of 3×3×1, which corresponds to a maximum k-point spacing of 0.4 Å-1 . The k-point mesh did not contain the Γ-point. These settings were determined by comparing energies using different numbers of k-points. All atomic structures of DSG were geometrically relaxed using the conjugate gradient algorithm . The ionic positions were fully relaxed until the forces were less than a tolerance of 10 -3 eV/ Å. All configurations of DSG used a vacuum spacing of 20 Å along the c axis to mitigate interactions between periodic images.