docs: note global AEC lookup under per-species explicit protocol

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: alongd

docs/source/advanced.rst

@@ -413,6 +413,14 @@ Internally each species is in one of three states: ``"inherit"`` (key absent),
 ``"opt_out"`` (explicit ``null``), ``"explicit"`` (preset name or recipe).
 These three survive ``as_dict`` / ``from_dict`` and restart-dict round-trip.
 
+.. note::
+
+   A per-species ``"explicit"`` protocol affects only that species' composite
+   energy: Arkane's atom energy correction (AEC) lookup still uses the
+   project-global ``sp_composite.base.level``, not the species-level base.
+   If a species needs AEC at a different level, set ``arkane_level_of_theory``
+   explicitly for the project.
+
 **Form 5 — W\ :sub:`n` family for high-accuracy anchor energies.** When
 δ-corrections beyond CCSD(T) are *not* the bottleneck and you mainly want a
 near-CBS CCSD(T) reference with the canonical core-valence and scalar-