For CTSH, although the total nuclear density is close to the exact results, the projected nuclear density shows more significant deviations. In particular, CTSH gives an extra WP component on the lower PES at t = 2500 au (see Figure ). The reason is that the reflected WP re-enters the interaction region with erroneous wave function, which is In Figure , we show channel populations as functions of the initial momentum k0 in the ECR model. When k0 < 28.3, the initial WP will split into two WPs and result in a reflected WP on the upper PES and a transmitted one on the lower PES. In these cases, decoherence is important since population transition between the two electronic states is significantly affected when the reflected WP re-enters the interaction region. FSSH provides accurate transmission populations but shows significant deviations in the reflection channels due to the overcoherence problem. CTSH gives better results for small k 0 , but improper decoherence may arise from the incorrect quantum momentum.