where can i find decap cells , are they defined in lib or lef.
They should be in both. I don't think there's a specific parameter that denotes decap cells - though I could be wrong.
If you have a hunch what their cell names might be, try searching for them in an active Encounter session like this:
encounter 1> dbGet head.allCells.name *DECAP*
Or look in the documentation provided by your library vendor.