For NaCl slit pores, T 1 extracted from MD is found to be quasi-independent from the frequency for ν ≤ 500 MHz, and to be very close to its bulk value T 1 ≈ 3.1 s (Fig. ). In contrast, for Na 2 SO 4 slit pores, T 1 increases from ≈ 2 s to ≈ 3 s as ν increases from 1.5 to 500 MHz. Therefore, the value of T 1 at the lowest accessible frequency in the simulations, ν = 1.5 MHz, is lower in the case of Na 2 SO 4 as compared to NaCl (Fig. ). For frequencies larger than ≈ 500 MHz, which corresponds to events whose duration is below ≈ 100 ps, T 1 strongly increases with ν for both NaCl and Na 2 SO 4 slit pores (Fig. ). This significant increase of T 1 for frequencies larger than ≈ 500 MHz is related to the molecular motion, and is also observed for bulk systems (see for instance Fig. ).