Can one be an atheist and believe in an afterlife?

[Alcon]

Short answer: no. Since atheism is a complete rejection of anything supernatural.

No, dude.  Theism is a belief in god(s); atheism is the absence of theism.  Atheism is not the "complete rejection" (whatever that means) of anything supernatural.  Atheism isn't necessarily the complete rejection of anything, besides the complete rejection of theism (definitionally).

[Alcon]

Short answer: no. Since atheism is a complete rejection of anything supernatural.

Not all atheists are the "I only believe in what science has proven" types.

You could not believe in a God, but believe an individual's identity can survive death in a phenomenon not yet proven by science.

I would contend that such a person is fooling themselves if they say they are atheist. They are rejecting a traditional notion of God, yet constructing a worldview that contains the core elements of a religion inhabited by divine beings.  Divine does not have to be omnipotent or omnipresent. So that person might be accepting divine beings that are just the post-mortal identities of people. That seems theist to me, just not monotheist.

In what sense is that theistic?  It's asserting metaphysical phenomena.  I think most people associate the term God (and theism) with some entity with some sort of non-ministerial powers over creation, not merely metaphysical phenomena that tend to go along with most theistic accounts.