Say, we dropped the bomb in open waters or somewhere visible enough for the coastal areas to see it or sent them a message recording how powerful of a weapon we've developed to scare them into surrender. Was that tried and if not, couldn't that have worked?
It was indeed considered, but then there are a lot of factors at play. More can be said on this matter if anyone else would like to put their oar in; for the meantime, u/restricteddata looks at the thinking behind the 'demonstration' thought and related matters. I highly recommend their blog as well, as linked there, and this section of the FAQ for a whole bunch of stuff on nuclear weaponry and the end of the Second World War.