For the simulator to work you must include a ground connection.
In SPICE analysis, the ground node (often designated as node 0) serves as the common reference point for all voltages in the circuit. It is essential because SPICE calculates voltages relative to this ground node. Without it, the simulator would have no reference for determining voltage levels, making the analysis impossible. It also helps ensure circuit stability and correct simulation results by providing a consistent point for voltage comparisons.
 No ground, simulation not possible |
 Ground present, simulation now possible |