I'm really enjoying my PhD but I feel a little lonely. I have many friends and I socialise a fair amount but I am getting frustrated in my attempts to meet somebody of the opposite sex. I'm a member of a few university societies but those are dominated by undergraduates. I do sometimes meet girls I think I would like in the department, or in another department, at seminars and so on, but I find they are always with a friend and so already in a conversation (or alternatively I'm already in a conversation with someone).

There's a girl I pass in the corridor maybe once every couple of weeks. Once she wasn't with people so I said "hi" and gave her a nice smile, but that's all... what am I supposed to do stop her and talk to her?

What do PhD students actually do to try and meet partners?