How to decline a postdoc interview if there is some possible future collaboration? I am applying for post-doc position. I was invited for two interviews on close dates. I already did the first one and got the job. I am going to accept the offer because the research is very nice, the institution has high publication-records and it is closer to my family. Unfortunately one of the tasks at this post-doc requires close collaboration with the second interviewer. My question is: 


how to inform the second interviewer that I got a post-doc position already? 
Should I go to the interview anyway, although I know I am going to reject the offer? 
Could I say something like: 


  Dear blablabla, In the past few days I was offered to work somewhere and I think I am going to accept the offer for personal reasons, but in any case, as our research is going to be close I would like to use my "interview-time" for giving a talk and know the research being conducted at your institute better?



Some of my colleagues told me that they have had very bad experience while rejecting job's offers or interview, so please, let's me know if you have been in a similar situation and which way you think is the less "harmful"?
Don't go -- it's a waste of everyone's time if you go to an interview without any intention of taking the job. People get (rightfully) more upset about you wasting their time than you not wanting a job because you've already found one elsewhere.

Besides, if you will be required to collaborate with the person with whom you were to have your second interview, they (i) may have personal contacts with the research group where you accepted the job, (ii) may already know that you took the first job, and (iii) will need to be among your friends. Simply inform them that you took the first job (and not beat around the bush by saying "somewhere" or "think I am accepting" when you have already accepted). Offering to come anyway for a collaboration or a seminar is fine.