When you give da’wah to atheists, give them five minutes of your time, then move on. If you can’t convince them in five minutes, you won’t be able to in five centuries.
As proof that you should focus your da’wah on other then atheists, consider the Qur’an. How many verses did Allah (سبحانه وتعالى) reveal to the Jews and Christians (People of the Book)? Countless. To the mushrikeen, the polytheistic Arabs? Dozens upon dozens. To the atheists? Three to seven.
Think about that. Three to seven verses only. Subhanallah. Why? Why so few?
Belief in Allah is self-evident. It’s part of the fitrah, the natural inclination of every human being. Someone who denies something so self-evident is not terribly intelligent, and definitely not worth spending effort on. (How long would you debate with someone who tells you, while outside on a sunny day, that the sun is not shining on them? Two seconds?)
Turn your purposes to more productive purposes and inshaAllah you will see more benefit from your actions.
May Allah (سبحانه وتعالى) purify our da’wah and accept our good actions, ameen.