You need to reach Rivet City and speak with Dr. Li, the next link in finding the location of your father.
When you speak with Li, she will tell you that your father moved to the Project Purity control room, located in the Jefferson Memorial. You can enter it from the gift shop entrance located on the west side of the building. There are Super Mutants within the building, equipped mostly with Nail boards, and the occasional hunting rifle.
When you reach the control room, you realize he isn't there, but there are holotapes giving clues to his location. Diary entry 10 within the set of tapes reports that he is heading to Vault 112 located to the west of Evergreen mills, hidden in a garage.
When you reach the garage and enter it, look for an electrical switch on the back wall to open the floor. Proceed down into the vault, and speak with a Robobrain. This Robobrain informs you that you arrived behind schedule (by approximately 202.3 years) and directs you to a tranquility module. Wear the jumpsuit, and enter the module to continue.