measure open loop gain
The 1F capacitor seems to indicate, that you are simulating rather than "measuring". It's O.K. of course, but should be mentioned to my opinion. If so, there are simple methods to determine open loop gain from a closed loop circuit simulation. without needing particular bias tricks.
A loop gain simulation is usually done in AC sweep mode, which implies small signal models and also that absolute signal amplitudes are meaningless. In a real circuit and in transient mode simulation (=large signal), you have to keep linear voltage range of course, so 100 mV input is a much too high magnitude.