Well my PhDs in a similar area, and I generally dress comfortably i.e. exactly the same as when I was an undergraduate (if they want me to look fabulous on a day-to-day level, they only need to increase my stipend...)!
When I have to interact with people outside the bubble (i.e anyone not from the department) in my capacity as a researcher, I basically go smart-casual. |I find that too smart tends to freak out the general public who then think you have to power analyses them and then section them...ah, how informed people are...
So yeah, for mooching around at work, where what you like, for working out of the Ivory Tower, nicely presented, but no scary suits