Three methods including the atomic resolved density of state, charge difference density, and the transition density matrix are used to visualize metal to ligand charge transfer （MLCT） in ruthenium（II） ammine complex. The atomic resolved density of state shows that there is density of Ru on the HOMOs. All the density is localized on the ammine, which reveals that the excited electrons in the Ru complex are delocalized over the ammine ligand. The charge difference density shows that all the holes are localized on the Ru and the electrons on the ammine. The localization explains the MLCT on excitation. The transition density matrix shows that there is electron-hole coherence between Ru and ammine. These methods are also used to examine the MLCT in Os（bpy）2（p0p）Cl （＂Osp0p＂： bpy=2,2-bipyrldyl; p0p=4,4＇- bipyridyl） and the ligand-to-ligand charge transfer （LLCT） in Alq3. The calculated results show that these methods are powerful to examine MLCT and LLCT in the metal-ligand system.
