Read NBANDS in io.vasp.outputs.Outcar init (#4195)

* add NBANDS parser

* add unit test

* test more vasp versions

* remove repeat default arg

* add overridden test

Author: DanielYang59

src/pymatgen/io/vasp/outputs.py

@@ -2149,7 +2149,15 @@ def __init__(self, filename: PathLike) -> None:
         self.final_fr_energy = e_fr_energy
         self.data: dict = {}
 
-        # Read "total number of plane waves", NPLWV:
+        # Read "number of bands" (NBANDS)
+        self.read_pattern(
+            {"nbands": r"number\s+of\s+bands\s+NBANDS=\s+(\d+)"},
+            terminate_on_match=True,
+            postprocess=int,
+        )
+        self.data["nbands"] = self.data["nbands"][0][0]
+
+        # Read "total number of plane waves" (NPLWV)
         self.read_pattern(
             {"nplwv": r"total plane-waves  NPLWV =\s+(\*{6}|\d+)"},
             terminate_on_match=True,
@@ -2183,7 +2191,6 @@ def __init__(self, filename: PathLike) -> None:
         # Read the drift
         self.read_pattern(
             {"drift": r"total drift:\s+([\.\-\d]+)\s+([\.\-\d]+)\s+([\.\-\d]+)"},
-            terminate_on_match=False,
             postprocess=float,
         )
         self.drift = self.data.get("drift", [])

tests/files/io/vasp/outputs/OUTCAR.nbands_overridden.gz

@@ -1327,6 +1327,22 @@ def test_onsite_density_matrix(self):
         outcar = Outcar(f"{VASP_OUT_DIR}/OUTCAR_merged_numbers2")
         assert "onsite_density_matrices" in outcar.as_dict()
 
+    def test_nbands(self):
+        # Test VASP 5.2.11
+        nbands = Outcar(f"{VASP_OUT_DIR}/OUTCAR.gz").data["nbands"]
+        assert nbands == 33
+        assert isinstance(nbands, int)
+
+        # Test VASP 5.4.4
+        assert Outcar(f"{VASP_OUT_DIR}/OUTCAR.LOPTICS.vasp544").data["nbands"] == 128
+
+        # Test VASP 6.3.0
+        assert Outcar(f"{VASP_OUT_DIR}/OUTCAR_vasp_6.3.gz").data["nbands"] == 64
+
+        # Test NBANDS set by user but overridden by VASP
+        # VASP 6.3.2
+        assert Outcar(f"{VASP_OUT_DIR}/OUTCAR.nbands_overridden.gz").data["nbands"] == 32
+
     def test_nplwvs(self):
         outcar = Outcar(f"{VASP_OUT_DIR}/OUTCAR.gz")
         assert outcar.data["nplwv"] == [[34560]]