Comparative analysis of analytical PES-based and direct dynamics approaches in gas-phase QCT simulations of the <b>F</b> − + SiH3I reaction

We present a comparative analysis of analytical potential energy surface (PES)-based and direct dynamics approaches within quasi-classical trajectory simulations of gas-phase reactions. Using the analytical PES of the F- + SiH3I reaction as a model system, we quantify how the two methods differ in reproducing relative energies along multiple reactive pathways. High-level composite coupled-cluster energies enable a systematic decomposition of trajectory energy errors into systematic and random components over more than 8000 geometries. The analytic PES exhibits primarily random, pointwise fitting errors with mean magnitudes comparable to or smaller than the systematic deviations characteristic of lower-level electronic structure methods used in direct dynamics. A strong correlation between stationary point energy errors and trajectory-level deviations offers a practical negative indicator for assessing PES reliability. Overall, the results demonstrate that well-fitted analytical PESs can achieve accuracy equal to or greater than that of low-level direct dynamics.