Extended Data Fig. 8: Stage-I [Br_0.5Cl_0.5]C_3.5 complex structures obtained from ab initio MD simulations.

Results from 30 ps of NVT ab initio MD simulations using the CP2K package and starting from a structure with homogenous –Br–Cl– bond lengths, as this structure was the most computationally efficient. a, Radial distribution function g(r) of stage-I [Br_0.5Cl_0.5]C_3.5 from 30 ps of MD simulations at 333 K (left) and final snapshot of the trajectory (right). b, DFT results for stage-I [Br_0.5Cl_0.5]C_3.5 from 30 ps of simulations at 333 K, following initial annealing at 633 K to accelerate the appearance of disorder (left) and final snapshot of the trajectory (right), with a close Br–Br contact highlighted in red. No close Cl–Cl contacts form at this voltage, as evidenced by the absence of features near the gas-phase Cl–Cl bond length in the radial distribution function. NVT simulations used the Langevin thermostat with an associated time constant of 10 fs and average box dimensions obtained from the equilibration runs performed in the NPT ensemble for 100 ps. A 1 fs timestep was used throughout. No signs of gassing and subsequent graphite exfoliation were observed over 100 ps of additional simulations under constant-pressure conditions, even after brief annealing at 633 K and relaxation back to 333 K.