Beej mantra for moksha or liberation should be used by only that person who has realized the futility of worldly life in real. This mantra is good for success in spirituality. The mantra should not be used after emotional problems, failure or fights etc. It should only be used when you truly want moksha.
Beej mantra for moksha is Hum. – हूँ।
Please note that beej mantra is a single letter powerful mantra. It should be chanted continuously for any number of times. When you chant it continuously, it takes a form. So the mantra should not be used for fun. It should only be used with intense longing for moksha.
There is no deity for this beej mantra. It is dedicated to the Supreme Truth.