Well, since the development of quantum physics, only in its most general sense. Now atoms are understood to be multiple, interacting, non-material shells of statistically probable energy waves which blink in and out of existence. That's hardly what they had in mind 2000 years ago.
The ancient Greek philosophers inferred the existence of atoms on sound principles and sound reasoning, granted that they didn’t know, and couldn’t know, very much about their nature, which knowledge was left to be discovered by far future generations. But this fact does not diminish, but only increases the status of their intellectual achievement, and properly leaves us in awe of them, and their time.
That's hardly what they had in mind 2000 years ago.
It's not what we have in mind today either, since virtually nothing in your summary describes the modern understanding of atoms.