If the simulation time is reduced by another factor of two (t max = 37.5 a.u.) then the peaks that constitute the near-edge merge together as shown in Fig. ; therefore, we take t max = 75 a.u. to be the minimum simulation length required for this particular application. At the SRC1-r1/6-311(2+,2+)G(d,p) level, this calculation involves 479 basis functions and the TDKS simulation requires 2.5 h (wall time) on a single compute node ) Other simulation parameters are the same as those described in Fig. and the spectrum for tmax = 600 a.u. is the same as that shown in Fig. . using 40 processor cores, or 100.6 h of aggregate computing time. (We have argued that aggregate computing time should be the measure of cost that is reported in high-performance computing. ) By contrast, LR-TDDFT/CVS calculations with 100 and 300 roots require only 14 and 35 min, respectively, on just 20 cores of the same hardware. For the calculation with 300 states, this is 11.7 h of aggregate computing time, or 12% of the TDKS cost. Note that frozen virtual orbital approximations (not used here) can further accelerate LR-TDDFT calculations, whereas no such approximation is available for TDKS simulations. 4.C.2. TiO 2 . We next consider the isolated TiO 2 molecule as a very simple example of a transition metal oxide. This is an interesting case because the metal L-edge overlaps with the oxygen K-edge in these nonrelativistic calculations. In general, L-edge spectra require the treatment of spin-orbit coupling, to describe the splitting of the 2p states into 2p 3/2 and 2p 1/2 , 3,35,99 but this is not considered in the present work where our goal is simply to compare TDKS and LR-TDDFT results and to emphasize the necessity of dipole filtering in the TDKS case.