Here are the conclusions to each of St. Thomas's "Five Proofs" of God's existence:
"...and this everyone understands to be God."
"...to which everyone gives the name of God."
"This all men speak of as God."
"...and this we call God."
"...and this being we call God."
A common criticism of this article is that there's no obvious connection between this "God of the philosophers" Whose existence St. Thomas argues for and the God of Abraham Who has revealed Himself, most definitively through His Son Jesus Christ. Christians don't give the name of God to the first efficient cause, they give the name of God to God. If God happens to also be the first efficient cause, so much the better for the philosophers' reasoning; if not, well, who really listens to philosophers anyway?
This leaves evangelical atheists in a tough spot. The being to which they give the name of God is, as it happens, God. Since they think God doesn't exist, they either a) think the first efficient cause doesn't exist; or b) think God isn't the first efficient cause.
Thinking the first efficient cause doesn't exist is a failure of human reasoning, and betrays the sort of hopeless metaphysics that makes reaching disagreement (rather than mere miscommunication) nearly impossible.
Thinking God isn't the first efficient cause is a mark of straight-up ignorance. When a grownup Christian's understanding of God is that of a second grader, it's regrettable, but he can still be a faithful Christian growing in holiness.
When a grownup evangelical atheist's understanding of God is that of a second grader, it's just embarrassing.