fix(lammps): distinguish neutral charge and dipole columns

dpdata/formats/lammps/lmp.py

@@ -70,6 +70,10 @@ def detect_atom_style(lines: list[str]) -> str | None:
                 # If it's a small float, likely a charge
                 if abs(val) < 10 and val != int(val):
                     return "charge"
+                # Neutral charge is numerically integral (0.0), but the
+                # decimal/exponent notation still identifies a charge column.
+                if any(ch in first_line[2].lower() for ch in (".", "e")):
+                    return "charge"
                 else:
                     # Likely molecule ID (integer), so bond/molecular style
                     return "bond"
@@ -327,6 +331,11 @@ def get_charges(lines: list[str], atom_style: str = "atomic") -> np.ndarray | No
 
 
 def get_spins(lines: list[str], atom_style: str = "atomic") -> np.ndarray | None:
+    # This branch predates explicit LAMMPS spin-style support and stores spin
+    # columns only in dpdata's legacy atomic layout. Other registered styles
+    # use their extra columns for unrelated physical quantities.
+    if atom_style != "atomic":
+        return None
     atom_lines = get_atoms(lines)
     if len(atom_lines[0].split()) < 8:
         return None

tests/test_lammps_atom_styles.py

@@ -237,6 +237,49 @@ def test_charge_style_no_comment_detection(self) -> None:
         """Test automatic detection of charge style without style comment."""
         self._test_style_parsing("charge_no_comment")
 
+    def test_neutral_charge_style_no_comment_detection(self) -> None:
+        """Integral-looking ``0.0`` charges must not be mistaken for bonds."""
+        path = "/tmp/test_neutral_charge_style.lmp"
+        self.test_files["neutral_charge"] = path
+        with open(path, "w") as fp:
+            fp.write(
+                """2 atoms
+1 atom types
+0.0 2.0 xlo xhi
+0.0 2.0 ylo yhi
+0.0 2.0 zlo zhi
+
+Atoms
+
+1 1 0.0 0.0 0.0 0.0
+2 1 0.0 1.0 1.0 1.0
+"""
+            )
+        system = self._load_system("neutral_charge")
+        self.assertIn("charges", system.data)
+        np.testing.assert_allclose(system["charges"][0], [0.0, 0.0])
+
+    def test_dipole_style_does_not_create_spins(self) -> None:
+        """Dipole moments are not magnetic spin vectors."""
+        path = "/tmp/test_dipole_style.lmp"
+        self.test_files["dipole"] = path
+        with open(path, "w") as fp:
+            fp.write(
+                """1 atoms
+1 atom types
+0.0 10.0 xlo xhi
+0.0 10.0 ylo yhi
+0.0 10.0 zlo zhi
+
+Atoms # dipole
+
+1 1 0.0 1.0 2.0 3.0 0.1 0.2 0.3
+"""
+            )
+        system = self._load_system("dipole")
+        self.assertIn("charges", system.data)
+        self.assertNotIn("spins", system.data)
+
     def test_bond_style_no_comment_detection(self) -> None:
         """Test automatic detection of bond style without style comment."""
         self._test_style_parsing("bond_no_comment")