LC Tank Circuit frequency error
Your circuit is faulty. During the two second charge period the net voltage across the inductor will be very close to 0 volts because the inductor acts as a short circuit at DC and when you open the switch, L1 and C1 will try and produce a decaying sine wave centred at 0 volts. This means your op-amp needs to be powered from a negative supply as well as a positive supply to avoid either destroying it and/or getting a sensible output: -