Potential energy surface

Once variational method is known to be quite good, I applied it to many systems.
Nakatuji-sensei said "oh you are doing chemistry" when I copying Herzberg, for geometries
of diatomic molecules.

When the system becomes larger, PQ conditions become worse.

Nakatuji-sensei told me that "why it's so good?" "I'm not sure, but I'm very sure that C2 are the first result that this method fails. because with PQ, I got 800% of correlation energy error"

However, fortunately or unfortunately, it was false. I got the correlation energy 108% or so...
Also staffs and colleagues told me about "double dissociation" or "triple dissociation". Surprisingly, PQG rules! The result was published as JCP 2002.