This is almost too embarrassing to ask but I looked far and wide and still could not figure out how to center a molecule on the center-of-gravity. Can someone help me out here ? Sorry if this is too trivial...

Hi, there is no such tool yet, even though it's a simple operation as you mentioned. Unfortunately I have no time to improve the GUI right now, I try to remember it next time I work with the GUI. Regards, TH