Molecular dynamics simulation on the dielectric properties of water confined in a nanospace between graphene and a h-BN substrate

Using a molecular dynamics simulation, we theoretically investigate the dielectric response of confined water intruded between graphene and a hexagonal boron nitride (h-BN) substrate. The dielectric constant of confined water with a thickness of 1 nm is only ε_r ∼ 2, which is much smaller than that of bulk water (e_r^bulk = 72.89). As the thickness h increases, ε_r begins to increase as well when h exceeds a few nanometers and then approaches e_r^bulk. The results of rotational autocorrelation functions suggest that the dielectric constant of the confined water is small because of the limited rotational degrees of freedom of the water on the graphene and h-BN substrate surfaces. In addition, the saturation electric field of the confined water with h < 100 nm is much higher than the breakdown electric field of the h-BN substrate (0.7 V/nm).