single supply opamp

If the + input is more negative than the - input then the output will head toward the most negative supply that the opamp's power pins are connected to. If the most negative supply is what you're calling "gnd" then that's the most negative voltage that the output can get to.

Typically, in a single-supply opamp that's hooked up in an inverting configuration, the + input is biased at the midpoint of the supply. For example, if the supply is 9V, then the + input will be set to 4.5V. If you then capacitively couple the - input (through the feedforward resistor) then the output will move up and down from its idle 4.5V point (as the input is driven with a changing signal).

An interesting thing happens if you capacitively couple the output. Then, you can get an output signal that goes more negative than your most-negative supply ("gnd", in your case). This is how car audio amplifiers can get speakers to move both outward and inward, on those type of amplifiers that require one side of the speaker to be connected to the minus side of the car's 12V battery (i.e., the car's chassis).

Bob