Did the Atom Bomb Prevent Russia From Conquering All of Europe?

Here's a passage from a book I read recently:

...a meeting of the Politburo in 1944 had decided to order the Stavka to plan for the invasion of France and Italy, as General Shtemenko later told Beria’s son. The Red Army offensive was to be combined with a seizure of power by the local Communist Parties. In addition, Shtemenko explained, ‘a landing in Norway was provided for, as well as the seizure of the Straits [with Denmark]. A substantial budget was allocated for the realisation of these plans. It was expected that the Americans would abandon a Europe fallen into chaos, while Britain and France would be paralysed by their colonial problems. The Soviet Union possessed 400 experienced divisions, ready to bound forward like tigers. It was calculated that the whole operation would take no more than a month…All these plans were aborted when Stalin learned from [Beria] that the Americans had the atom bomb and were putting it into mass production.’Stalin apparently told Beria ‘that if Roosevelt had still been alive, we would have succeeded’. This, it seems, was the main reason why Stalin suspected that Roosevelt had been secretly assassinated.

-Historian Antony Beevor from the book