Using keyword only arguments for tip_height, current, and supercell a…

…rguments

Co-authored-by: Martin Schlipf <[email protected]>

src/py4vasp/calculation/_partial_charge.py

@@ -108,6 +108,7 @@ def to_dict(self):
     def to_stm(
         self,
         selection: str = "constant_height",
+        *,
         tip_height: float = 2.0,
         current: float = 1.0,
         supercell: Union[int, np.array] = 2,