Within FSSH or any FSSH-like algorithm, one always separates the electronic quantum subsystem from the nuclear classical coordinates ( ⃗ R, ⃗ P ). The total Hamiltonian for the full system is H( ⃗ R, ⃗ P ) = α (P α ) 2 /2M α + H ele ( ⃗ R) where H ele ( ⃗ R) is the electronic Hamiltonian.