We first verify that the value ∆t = 0.1 a.u. is suitable to obtain a stable simulation. Using the impulse field that is plotted in Fig. , we performed a TDKS simulation using values of ∆t ranging from ∆t = 0.01 a.u. (= 0.242 as), corresponding to a Nyquist frequency of 8.5 keV, up to as large as ∆t = 0.2 a.u. (= 4.84 as), corresponding to a Nyquist frequency of 427 eV. Since the external field is applied in the z direction, corresponding to the internuclear axis of H 2 , we can use µ z (t) to assess the impact of ∆t. This quantity is plotted in Fig. for simulations using three different time steps and the results track one another quite well. Taking the smallest time step (∆t = 0.01 a.u.) as the benchmark, differences in µ z for the larger time-step simulations are on the order of 10 -4 a.u., in a total dipole moment whose magnitude ranges almost to 0.4 a.u.. If the time step is increased to ∆t = 0.2 a.u. then the deviations in µ z increase in mag- The simulations use the impulse field shown in Fig. and the ∆t = 0.01 a.u. data are the same as those plotted in Fig. . For clarity, only a portion of the simulation is shown but these simulations have the same t = 0 starting point as those in Fig. .