How should one deal with an atheist?

People should be dealt with according to what serves the best interest, without violating Allah's command. The person mentioned can be treated by constantly reminding him of Allah, explaining His names and attributes, focusing on His power, believing that giving and withholding are in His hands, and having certainty in divine decree. One can also seek assistance in changing his behavior by commanding him to frequently engage in worship and remembrance, while observing Allah's blessings upon all creatures and how He has guaranteed their sustenance, citing His words, the Almighty: "And there is no creature on earth but that upon Allah is its provision. And He knows its resting place and its depositing place. All is in a clear register."