Testing spice model for common mode rejection ratio?

Question

I've been trying to create a circuit to simulate common mode rejection ratio of an op amp to test the spice model's accuracy. While I've seen online that being able to use exact resistors only a simulator could use can be very helpful in determining CMRR, I can't seem to get a circuit to work. Anything I try either doesn't converge in simulation or doesn't give an accurate results. Any help would be appreciated.

EDIT:

^{simulate this circuit – Schematic created using CircuitLab}

I included a circuit schematic of my most recent iteration. I figured that I would extract the AC RMS voltage from the input vs output and calculate the common mode gain from the circuit. I first had the R2 resistor grounded but thought after that it should be ground w.r.t the AC common mode signal, so I attached it to my common mode signal generator.

I think it might be worth mentioning that at first I tried to connect a sine wave into the input rails via two 1k resistors and measured the open loop gain but it didn't converge.

Answer 1

Use this circuit (and equation) instead:

Source: https://www.analog.com/media/en/training-seminars/tutorials/MT-042.pdf

It should be easy to come up with resistors in spice that are matched (in real life not so much and so you should use the other circuit in the application note).

This has worked for me, if it doesn't work the model may not be that realistic.

Another note: While the diagram shown in the OP has no ground on the 18V supplies, I hope that there was a ground between the supplies in the spice netlist. Otherwise spice would have a very difficult time finding the DC operating point and simulating, as al the voltages of that portion of the circuit would be floating, and the simulation wouldn't function very well. Supplies need to be referenced from ground, which I hope was done.