We once had a 'strong atheist" come to SMP who left in dismay as to what people perceived to be atheism. His approach, which is classical, is that there are no spirits, no gods,no supersensible entities,no demons,no souls, nor anything in thought nor action which was of a supersensible nature. This crashes down into a strict materialism( as he saw it) in which only the weights and measurements of materialism is hegemonic.
In effect, as above,we are only in past , present and future a conclave of elements of sodiums, potassiums, and magnesiums,etc. only to degenerate into the cosmic welter of materiality at our death.
Of course, from my perspective, the above is only theoretical materialism which gives some hope to proper sight. If one is an atheist as responsive personally to a particular religion such as Christianity then one must consider whether he is an AntiChrist or just doesn't happen to like the local Baptists.