Once is solution is iterating, the solution can be interrupted by clicking on the
(Stop) button in the toolbar. The solution can be resumed again by running or stepping.
This may cause the time-step to be incomplete for transient simulations, since the solution may be stopped during an inner iteration. In this case, a message similar to the one below will appear in the Output window.

As indicated, stepping the solution once will complete the time-step.
Although primarily intended for batch operation, the stop file stopping criterion will also work while the solution is iterating interactively.