Interesting topic. I do not believe there are any true "100%" atheist. I have talked to individuals that proclaim to be an atheist. If you talk to them long enough, you will find that some tragic event took place in their life and now the deny God, out of rebellion. They do not deny the total existance of God. Most of their conversations uses the word "IF" which means that there is some doubt in their mind on the existance of God.
I had a co-worker, who proclaimed to be an atheist. I ask him why, he stated "My mom died from cancer. I prayed everyday asking God to save her and she died anyway. Why, should I believe God?" My question to him was - how and why would pray to someone that do not exist. That proves to me that you believe in "God, Jehovah or Elohim" and the only reason that you are saying that you do not belive, is due to the death of your mother.
Several months later he admitted, that he believed in the existance of God. But, did not understand why his mother died.