Are you saying the PRIMARY reason for the use of the Atomic bombs was to convince the Russians that we would use them - ?
Ike even said so and so did MacArthur and many other military leaders.
They knew that FDR was weak and near death at the Yalta conference. That's why the US gave away Eastern Europe.
Stalin basically over ran FDR and even Churchill made mention of that.
Truman knew that Stalin was crazy and killing millions of Russians.
Truman felt that the US needed to show Stalin that we not only had the technology, but the will to use the Atomic Bomb.
Truman had to make up for the weakness of FDR at Yalta and to show Stalin at Potsdam that he was one tough little SOB.