Looking for advice here. After beginning a 1-year gap year research position with a successful project and poster presentation of the results, I decided to switch labs, as I was not fitting in well with the PI's style of management/culture of the lab and knew I'd have a better experience and better research in a different lab. As it turns out, I actually switched into a lab run by the department chief (my old PI's boss), who offered to write me a recommendation for the duration of my post-bacc. Seeing as how I don't plan to include a rec.letter from the previous PI (it would not be good/strong), should I still list this poster presentation on my work/activities section - I presented it at a national conference - and, if so, could I list the department chief as one of the author's? If not, any suggestions as to how to avoid/explain potential red flags in that I'm not including a letter from this prev.research supervisor?