Withdrawing my application for a research fellowship when getting a job elsewhere While waiting for the outcome of my application for a research fellowship, I was offered a job at a university in another country. It turned out that my fellowship application passed the first stage, but after some consideration, I decided to accept the job offer and not to pursue my fellowship application any further. My question is, should I tell the secretariat immediately that I would like to withdraw my application or should I just let the deadline for the second stage of application pass without informing them anything? Also, what should I say to my potential collaborators?
It is customary to withdraw your application(s) as soon as you have accepted a post elsewhere. By doing so you increase the chances of fellow applicants to be shortlisted / admitted to the next stage.  Also, non-attendances and late withdrawals create a considerable mess at the interview stage, and it is better not to annoy your prospective colleagues, with some of which you may need to collaborate in future. 

Actually, prompt communication is typically a win-win situation, and unnecessary delays in communication usually give nothing good to anyone (despite maybe some illusion of control).