I'm using a single supply op amp. Specifically the LM2904NG. I am trying to invert 0.67 V to -0.67 V. My output is in fact positive. I simulated the first single supply op amp I could find (LT1006) in LTspice in order to see if I could figure it out. I started with just trying to invert 3.3 V before adding in more circuitry but it does not work. It outputs 136 mV in fact.
My expectation is that the output will be where Rf=R4 and Rin=R1. This is not the case. Am I missing something basic about single supply op amps? Can these not provide a voltage below their negative rail? I suppose this seems reasonable.