The dynamical entanglement for Fermi coupled C-H stretch and bend vibrations in molecule CHD 3 is studied in terms of two negativities and the reduced von Neumann entropy,where initial states are taken to be direct products of photon-added coherent states on each mode.It is demonstrated that the negativity defined by the sum of negative eigenvalues of the partial transpose of density matrices is positively correlated with the von Neumann entropy.The entanglement difference between photon-added coherent states and usual coherent states is discussed as well.
