I did my dissertation on the atomic bombing of Japan so have read a lot of the original sources. There wasn’t really any discussion on whether they should drop the bombs or what the aims of them would be. Nearly all of the discussion was on how they would be dropped and what the target would be. They chose the two targets for 2 main reasons; they were relatively untouched by the war so the destructive force the bombs could be seen, and they were big enough targets to hit and there was nothing to stop the blast e.g. mountain ranges.
The main reason they wanted these criteria was to shock the Japanese government (and possibly the Soviets). They deliberately picked civilian targets to do this.
There was no mention (in the documented history, at least) of them expecting unconditional surrender as a result of the bombing. They used the bombs simply because they had them and saw no reason not to. If it was simply the shock they wanted to scare the Japanese into surrender then the declaration of war from the Soviets could potentially have also worked. The declaration wasn’t a surprise to the Americans, they’d been discussing with them for months, although the timing was probably brought forward by Hiroshima.
After the event, a lot of the leading military figures came out against the need to use the bomb, although of course this is “what if” history. But the idea that they wouldn’t have surrendered without it is also guess work. As others have said, they’d twice approached the US indirectly with offers of peace, although not unconditional surrender. So the idea of them been willing to surrender wasn’t exactly unknown.
In regard to the random photos of Japanese military atrocities, I’m not sure what the point you’re trying to make is. Yes, their army committed some horrendous war crimes against both POWs and civilians, but I’m not sure how that justifies nuking a city full of civilians. If the mass murder of civilians is bad, then it’s bad regardless of the nationality doing it (see also Dresden and Katyn for other examples).