fix Ion parsing bug introduced by commit

materialsproject@b4a70ee

src/pymatgen/core/ion.py

@@ -173,7 +173,8 @@ def get_reduced_formula_and_factor(
         el_amt_dict = {k: int(round(v)) for k, v in comp.get_el_amt_dict().items()}
         formula, factor = reduce_formula(el_amt_dict, iupac_ordering=iupac_ordering)
 
-        if (self.composition.get("H") and self.composition.get("O")) is not None:
+        # This line checks specifically that the contains an equal amount of O and H. When that is the case, they should be displayed as "OH" rather than "HO".
+        if (self.composition.get("H") == self.composition.get("O")):
             formula = formula.replace("HO", "OH")
 
         if nH2O > 0:
@@ -187,6 +188,13 @@ def get_reduced_formula_and_factor(
         elif formula == "H2CO":
             formula = "CH3COOH"
             factor /= 2
+        # phosphoric acid system
+        elif formula == "PH3O4(aq)":
+            formula = "H3PO4(aq)"
+        elif formula == "PHO4[-2]":
+            formula = "HPO4[-2]"
+        elif formula == "P(HO2)2[-1]":
+            formula = "H2PO4[-1]"
         # acetate
         elif formula == "H3(CO)2":
             formula = "CH3COO"

tests/core/test_ion.py

@@ -61,6 +61,7 @@ def test_special_formulas(self):
             ("N2", "N2(aq)"),
             ("H4O4", "H2O2(aq)"),
             ("OH-", "OH[-1]"),
+            ("H2PO4-", "H2PO4[-1]"),
             ("CH3COO-", "CH3COO[-1]"),
             ("CH3COOH", "CH3COOH(aq)"),
             ("CH3OH", "CH3OH(aq)"),