There's no scientific evidence for the existence of a deity of any sort. Furthermore, there is nothing known about the universe that demands the existence of one. In fact, the existence of a deity raises more questions than it would solve; Occam's razor therefore tells us that the existence of one is rather unlikely.
It's not impossible, but is A) completely unproven and B) rather improbable. Therefore, belief in the existence of a deity of any sort is intellectually unsound.
A rapid summary of the arguments of Dawkins, Hitchens, Harris, so on.