op-amp thevenin resistance calculation in pspice
Because negative feedback is used in this op-amp circuit, the op-amp's massive open-loop gain ensures that the effective output impedance of the circuit is very close to zero ohms. As frequency rises, the op-amp open-loop gain falls at 6 dB/octave and the output impedance rises.
However, if you are just interested in DC or low-frequency conditions, you can assume that the open-loop gain is high enough to make the circuit's output impedance below 0.1 ohms (but don't assume a typical op-amp circuit can deliver amps of current because it cannot).

op-amp thevenin resistance calculation in pspice

If you wanted to determine this in PSPICE, then you could attach a load resistor to the output and see how much the voltage changes. That change in voltage divided by the change in output current (when you apply the load) is the dynamic output impedance of the circuit.