can lead to significant deviations in first-order gradients of the nuclear density distribution. Consequently, the quantum momentum may undergo notable changes and result in qualitatively inaccurate decoherence strength. This feature makes the decoherence process parameter-dependent to some extent. To obtain accurate quantum momentum, we propose a new approach to reconstruct the nuclear density, which can make the gradient smoother and match better with the exact solution. In detail, we group the trajectories on each PES into several clusters and approximate each cluster as a Gaussian distribution function. As the properties of a trajectory generally undergo minor changes during a short time interval, we do not need to re-group the trajectories at every time step during the simulation. The grouping criterion guarantees that the trajectories within a specific cluster are close in the real space with similar momentum direction and occupy the same active state. New clusters are generated when trajectory reflection or surface hops happen. A step-by-step outline of our trajectory clustering algorithm can be found in the Supporting Information (SI).