What then? If some did not believe, their unbelief will not nullify the faithfulness of God, will it? May it never be! Rather, let God be found true, though every man be found a liar, (Romans 3:3-4a NASB)
The unbelief of an atheist doesn’t nullify GOD in any measure or implication; it only minimizes the atheist’s mind, hardens the atheist’s heart, limits the atheist’s life, and reduces the atheist’s usefulness – and ultimately proves the atheist to be a fool.
The fool has said in his heart, “There is no God.” (Psalm 14:1a NASB)