[mlechha]

It's not about being an atheist per se, but about believing. The others I'm sure strongly believed in something, which kept them going. Landau for example had physics to occupy him and keep him sane.

[varjag]

IMO that's not quite the same. Doing physics isn't "believing" in physics, but sure keeping yourself focused on something goes a long way.

Likhatchev deathbed words to his crying wife were "don't get so upset, it's just the matter changing its state".