Here is the selection for the engineer (civil, chemical, mechanical), computer scientist/hacker, and inventor costumes:
These costumes should be pretty easy to figure out. If your character is a chemist/chemical engineer/pharmaceutical scientist - opt for the mad scientist costumes or just throw on a white lab coat.
For the robotics engineers/mechanical engineers - you can wear the lab coat or dress as one of your robot inventions and get a laugh or two.
Computer scientists and hackers can be silly with the floppy disk costume, a lab coat (as you might be working in a clean room), or wear a black hoodie with the Mr. Robot mask. The other mask you can wear is a Guy Fawkes, but there are no links above for that.
With any of these super smart roles, you can always just opt for a traditional nerd with high-water pants, button up shirt, bow-tie, and glasses with white tape on the bridge.
Or for the inventor roles, go for the lab coat, the nerd, or give a nod to the historical inventors.