Should I include a synonym in parenthesis in abstract of a PhD thesis? Should I include in parentheses a synonym I will use in the main text already in the abstract?
Example:

The atomistic scale (micro-scale) shall be considered ...
The atomistic scale shall be considered ... (Then introduce the synonym in the main text?)
You can always edit an abstract slightly to your benefit using square brackets:

The atomistic [micro-]scale shall be considered.

It's a widely accepted way of editing abstracts to help with context.
For example it's used when written news wants to add clarity to direct quotes.