I don’t understand how because a mathematical technique has existed since the 1800s, it makes sense to use it in a physics setting. This does not seem like an argument.

Also, you say that his calling the Karpus and Kroll result a fraud is “libel,” but the paper references “Karplus and Kroll confessed that they had not independently reached the same result; instead, they had reached a consensus result.”

There’s even a Feynman quote saying, “It turns out that near the end of the calculation, the two groups compared notes and ironed out the differences between their calculations, so they were not really independent.”

You seem to be trying to discredit this paper. Why is that so? Trying to frame it as “libel”, in particular, is quite ridiculous in this setting and seems to betray some personal wish for the author to be punished for his audacity of criticizing physics research.