Bugs in Composition().__ge__() method

[txy159]

Python version

Python 3.9

Pymatgen version

2024.3.1

Operating system version

macos

Current behavior

Expected Behavior

The second one should output False.

Minimal example

from pymatgen.core import Composition

Composition("LiFePO") >= Composition("LiFeP")

Composition("LiFePO") >= Composition("LiFeH")

Relevant files to reproduce this bug

No response

[DanielYang59]

Admittedly the behaviour is surprising, but I believe this is expected, I had the same question in #3895

This comparison operation is not defined to really "compare" Composition (it might not make chemical sense to order compositions in the first place), but more to provide a stable ordering reference (such that when you sort compositions, they don't came out in a unpredictable/random pattern).

pymatgen/src/pymatgen/core/composition.py

Lines 234 to 241 in 31f1e1f

	def __ge__(self, other: object) -> bool:
	"""Composition greater than or equal to. We sort the elements in the compositions in order of
	electronegativity. The amount of the most electropositive element that is not equal within a certain
	tolerance factor is used to make a comparison. Note that an element not present in a Composition has an implied
	amount of 0.
	Should ONLY be used for defining a sort order (the behavior is probably not what you'd expect).
	"""

Note the elements are sorted by electronegativity, in this case the comparing order is [Element Li, Element Fe, Element P, Element H, Element O].

For the first comparison, the oxygen in "LiFeP" has an implied amount of zero (LiFePO₀), it's therefore considered "smaller" than "LiFePO".

For the second case, the amount of P is greater in "LiFePO" than "LiFeH" (effectively LiFePH₀O vs LiFeP₀HO₀) and thus the short-circuit:

pymatgen/src/pymatgen/core/composition.py

Lines 245 to 249 in 31f1e1f

	for el in sorted(set(self.elements + other.elements)):
	if other[el] - self[el] >= type(self).amount_tolerance:
	return False
	if self[el] - other[el] >= type(self).amount_tolerance:
	return True