Chemistry is applied physics. Chemistry answers that H2 and O2 can be joined to form water under certain conditions, but doesn't answer the "Whys"
Physics answers that. And the answer goes around orbitals, energy states, electrons, etc.
Chemistry does answer the whys beyond product yields, why certain elements react is vastly covered throughout organic, inorganic & physical chemistry . It is the basis of these sub-fields, and how this is determined is looking at orbitals, energy states etc...
So, Pauli's exclusion principle is Physics or Chemistry? I'd say it's "both".
I never said reductionism is a one way street.
But in simulations you usually work bottom-up (in abstractions). Of course, sometimes you can't do that, because it's overly complex.
My field (electrical engineering) has a lot of physics as well and I don't mind if those who invented the techniques I use were physicists or engineers (or something else), or if such and such things are in the "engineering" domain or the "physics" domain, I just use them. The point is moot.
Today is a great day for computational chemistry. It is good to see the detailed Nobel announcement acknowledge other stalwarts of the field like Peter Kollman (who created AMBER, a package similar to CHARMm by Karplus et al). I have no doubt that Kollman would have received this prize had he been alive today.