All the atheists I know simply do not believe God does exist. T here is a big difference between positively believing that a thing does not exist, and simply lacking belief in it's existence. If you describe your God with self-contradicting attributes which make it logically impossible, then I may safely say that such a thing does not exist as described. This is not faith - this is reason. These are two different answers.
Nobody disbelieves in unicorns purely as a matter of personal faith .
A gain, apply the same reasoning to the Gods of other religions. I f my atheism with respect to your deity is a religion, then your atheism with respect to other deities is also a religion. A theism is neither religion nor faith, but the happy freedom from them.