where ⃗ r i is the position of the ith atom, q i is its (corrected) partial atomic charge from our model, and the summation is over all the atoms in the system. Different from that of a rigid non-polarizable model, the time dependence of the total dipole arises from not only the atomic motion (i.e., r i (t)), but also the fluctuating charges (i.e., q i (t)).