Kickstarting an opamp for oscillating?
Most OpAmps aren't meant to be used as comparators because many have 'Clamp Diodes' used for protection in their input stages which can become a problem in this use case, there are some exceptions like LM358 and the ever-popular ua741, while Op Amps like TL072 do have them (you can tell its datasheet specifies the Clamp Current), but keep in mind also manufacturers aren't usually at always specifying this.

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You can also think of a Schmitt-Trigger as a 'Specialized OpAmp Circuit' which amogst other things wouldn't have 'Clamp Diodes' at the input. You can check one of my other replies where I go into a lot more details on how is the Schmitt-Trigger designed using an OpAmp.

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Another thing to keep in mind is that oscillators depend in a 'Closed Loop Gain' of system, and while an ideal OpAmp has a constant 'Closed Loop Gain' to infinity real Op Amps don't because they are limited by the 'Open Loop Gain', it could be the case you are using an ideal OpAmp in your simulations, or the model might, or not be completely accurate.

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Finally, it is likely that as you increase frequency, the 'Closed Loop Gain' becomes less than one, at which point you will have a "Damp Oscillator", causing the oscillation to die down eventually.

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If you want more details:


Op Amps used as Comparators—is it okay?
Oscillator Operation