Indeed highly effective. But as he himself admitted caused signicant civcilian fatalities

I may have posted this elsewhere, but once again, just so we are all on the same page:

End of WW2.

1944: Imperial Japanese government begins to put out vague queries for an armistice to give their industry time to rearm. No discussion of surrender.

May 8 1945: Last remnant of Nazi military surrender unconditionally. Japan remains the last Axis power.

July: Intense air raids and naval bombardment of Japan show invasion is imminent. Japanese military calls up all males 17 to 60 and females 17 to 45 for militia.

Approximately 10,000 varied aircraft are prepared for suicide defence. Adults and children are trained as suicide bombers to wear explosive vests.

July 16: Trinity A-bomb successfully tested in the USA.

July 26: Potsdam Declaration demands immediate unconditional surrender of Imperial Japanese Forces, “or face prompt and utter destruction.”

August 1: OWI leaflet #2106 is dropped over target cities in Japan including Hiroshima and Nagasaki warning to evacuate before bombing begins. On the same day Emperor Hirohito gives the order to kill all 40,000 slave labour Allied prisoners if the Americans land on Japanese soil. At the time these slaves were being starved to death anyway.

August 6: Hiroshima uranium-bomb detonation.
 
August 7: Japanese physicists examine the ruins of Hiroshima and informs the Chief of Staff that it is the result of a nuclear weapon. Naval Chief of Staff Toyoda calculates that the USA can only have built two or three bombs and that while it means great loss of life, there is no reason to halt the war.

Prime Minister Suzuki tells Japanese press the government will ignore Allied demand for surrender.

August 9: Nagasaki plutonium-bomb detonation.
Minister of War tells Hirohito he did not feel the A-bombs made surrender necessary. Saner ministers convince the Emperor to surrender. PM Suzuki is prepared to carry out Imperial instructions. 

August 14: Ministry of War and officers of the Imperial Guard attempt to overthrow the government and prevent surrender. The coup fails. Attempted assassination of Suzuki fails.

August 15: Hirohito’s recorded announcement of cease fire is broadcast over Japanese radio. There is no mention surrender in the communique.

Whether the bomb change Stalin's mind is irrelevant to the War against Japan. Japan was not seen a mix of good and bad,. Their cruel and fanatical conduct in China and WW2, convinced most people in the Western world, China, the East Indies, and the Pacific Islands, that Japan deserved to be flattened.