Hi everyone
I've applied for the first time for an advertised PhD program got a interview but been rejected after the interview,by an email saying that "you been unsuccessful on this occasion" so should I write them back and ask them for feedback?or a thank you note? or should I just leave it ?
Thank you

Sorry to hear that. Don't give up!

There are no hard fast rules. It is always courtesy to say thanks in my humble view. And if you want feedback, you've every right to ask for it - they may give some and it may even be helpful.

Sorry to hear that and good luck for future interviews! I agree with Tudor_Queen and personally I always, always ask for feedback. I think it's a great way to find out what you could improve on next time. I know it's gutting and it's a cliche but really, learning from it is the best thing you can get out of it! :)

Sorry to hear about that. Agree with both the responses. It is always beneficial to ask for a feedback. I have served on the admission committee as a graduate student and was shocked to see how the process works. Which PhD program and university you have applied to?

Thank you everyone for your answers . I felt a bit sad after their email
the thing is when the Interview panel were just the supervisors of the program but I got the email from the school Administrator ,so to whom should I write ?and any ideas for a good email?

I would write to the admin and ask for feedback and they should contact the supervisor for you.

One thing that always works for the admission is to try to get in contact with a faculty way, way ahead of time. Express interest in their work and come up with some teeny-tiny (it can be silly) research idea in the same/related field. Try to talk (skype) to this professor before you start your application process. When a Professor makes a personal recommendation to the admission committee it is rarely rejected. Make sure your references give you shining recommendation. These are the two most important things. One personal advise for the interview, do not underplay yourself. Don't be humble, be moderate.

You must say thanks in reply but also you ask them for feedback. This will help you in future interviews. This way you will able to know that what the really problem in your interview, that will not happen again.

My advice, like everyone else who has this far replied, is to not give up. With my first PhD interview I got all the way to the final stage, a decision between two final candidates for the project, before I lost to someone else. I searched around and wrote a few more applications and eventually, on my third application, got accepted with full funding, so definitely keep trying.

My advice is to send an email, thank them for the opportunity, and ask, if possible, for feedback. When writing an application to a specific institution contact them first. Explain the research and ask if it is relevant to the department. A number of universities I thought would be good choices for my research wrote back saying that they were not the best choices and suggested other places.

Don't be anxious, rejection doesn't mean that you are not capable of doing a PhD. I advise you to keep trying until you received a confirmation.