diff --git a/pymatgen/io/lammps/data.py b/pymatgen/io/lammps/data.py
index c08d284e748..7ca174ab59c 100644
--- a/pymatgen/io/lammps/data.py
+++ b/pymatgen/io/lammps/data.py
@@ -37,7 +37,7 @@
 
 if TYPE_CHECKING:
     from collections.abc import Sequence
-    from typing import Any, Self
+    from typing import Any
 
     from pymatgen.core.sites import Site
     from pymatgen.core.structure import SiteCollection
@@ -639,7 +639,7 @@ def label_topo(t) -> tuple:
         return self.box, ff, topo_list
 
     @classmethod
-    def from_file(cls, filename: str, atom_style: str = "full", sort_id: bool = False) -> Self:
+    def from_file(cls, filename: str, atom_style: str = "full", sort_id: bool = False) -> LammpsData:
         """
         Constructor that parses a file.
 
@@ -1204,7 +1204,7 @@ def to_file(self, filename: str) -> None:
             yaml.dump(d, f)
 
     @classmethod
-    def from_file(cls, filename: str) -> Self:
+    def from_file(cls, filename: str) -> ForceField:
         """
         Constructor that reads in a file in YAML format.
 
@@ -1217,7 +1217,7 @@ def from_file(cls, filename: str) -> Self:
         return cls.from_dict(d)
 
     @classmethod
-    def from_dict(cls, d: dict) -> Self:
+    def from_dict(cls, d: dict) -> ForceField:
         """
         Constructor that reads in a dictionary.
 
@@ -1416,7 +1416,7 @@ def parse_xyz(cls, filename: str | Path) -> pd.DataFrame:
         return df
 
     @classmethod
-    def from_files(cls, coordinate_file: str, list_of_numbers: list, *filenames) -> Self:
+    def from_files(cls, coordinate_file: str, list_of_numbers: list, *filenames) -> CombinedData:
         """
         Constructor that parse a series of data file.
 
@@ -1442,7 +1442,7 @@ def from_files(cls, coordinate_file: str, list_of_numbers: list, *filenames) ->
     @classmethod
     def from_lammpsdata(
         cls, mols: list, names: list, list_of_numbers: list, coordinates: pd.DataFrame, atom_style: str | None = None
-    ) -> Self:
+    ) -> CombinedData:
         """
         Constructor that can infer atom_style.
         The input LammpsData objects are used non-destructively.
diff --git a/pymatgen/io/lammps/inputs.py b/pymatgen/io/lammps/inputs.py
index 4208c36afb3..7ec83f71c97 100644
--- a/pymatgen/io/lammps/inputs.py
+++ b/pymatgen/io/lammps/inputs.py
@@ -27,7 +27,6 @@
 
 if TYPE_CHECKING:
     from os import PathLike
-    from typing import Self
 
     from pymatgen.io.core import InputSet
 
@@ -539,7 +538,7 @@ def write_file(self, filename: str | PathLike, ignore_comments: bool = False, ke
 
     @classmethod
     @np.deprecate(message="Use from_str instead")
-    def from_string(cls, *args, **kwargs) -> Self:
+    def from_string(cls, *args, **kwargs) -> LammpsInputFile:
         return cls.from_str(*args, **kwargs)
 
     @classmethod
@@ -918,7 +917,7 @@ def md(
         temperature: float,
         nsteps: int,
         other_settings: dict | None = None,
-    ) -> Self:
+    ) -> LammpsRun:
         r"""
         Example for a simple MD run based on template md.template.
 
diff --git a/pymatgen/io/lammps/outputs.py b/pymatgen/io/lammps/outputs.py
index 7bc3b660ee6..5d7237bc222 100644
--- a/pymatgen/io/lammps/outputs.py
+++ b/pymatgen/io/lammps/outputs.py
@@ -18,7 +18,7 @@
 from pymatgen.io.lammps.data import LammpsBox
 
 if TYPE_CHECKING:
-    from typing import Any, Self
+    from typing import Any
 
 __author__ = "Kiran Mathew, Zhi Deng"
 __copyright__ = "Copyright 2018, The Materials Virtual Lab"
@@ -48,11 +48,11 @@ def __init__(self, timestep: int, natoms: int, box: LammpsBox, data: pd.DataFram
 
     @classmethod
     @np.deprecate(message="Use from_str instead")
-    def from_string(cls, *args, **kwargs) -> Self:
+    def from_string(cls, *args, **kwargs) -> LammpsDump:
         return cls.from_str(*args, **kwargs)
 
     @classmethod
-    def from_str(cls, string: str) -> Self:
+    def from_str(cls, string: str) -> LammpsDump:
         """
         Constructor from string parsing.
 
@@ -76,7 +76,7 @@ def from_str(cls, string: str) -> Self:
         return cls(timestep, n_atoms, box, data)
 
     @classmethod
-    def from_dict(cls, d: dict) -> Self:
+    def from_dict(cls, d: dict) -> LammpsDump:
         """
         Args:
             d (dict): Dict representation.
diff --git a/pymatgen/io/lammps/sets.py b/pymatgen/io/lammps/sets.py
index 2f3edd78692..3f56a3c370a 100644
--- a/pymatgen/io/lammps/sets.py
+++ b/pymatgen/io/lammps/sets.py
@@ -19,7 +19,6 @@
 
 if TYPE_CHECKING:
     from pathlib import Path
-    from typing import Self
 
 __author__ = "Ryan Kingsbury, Guillaume Brunin (Matgenix)"
 __copyright__ = "Copyright 2021, The Materials Project"
@@ -73,7 +72,7 @@ def __init__(
         super().__init__(inputs={"in.lammps": self.inputfile, "system.data": self.data})
 
     @classmethod
-    def from_directory(cls, directory: str | Path, keep_stages: bool = False) -> Self:
+    def from_directory(cls, directory: str | Path, keep_stages: bool = False) -> LammpsInputSet:
         """
         Construct a LammpsInputSet from a directory of two or more files.
         TODO: accept directories with only the input file, that should include the structure as well.
diff --git a/pymatgen/phonon/bandstructure.py b/pymatgen/phonon/bandstructure.py
index 06652afa6cf..e4835d21dfb 100644
--- a/pymatgen/phonon/bandstructure.py
+++ b/pymatgen/phonon/bandstructure.py
@@ -14,7 +14,6 @@
 if TYPE_CHECKING:
     from collections.abc import Sequence
     from os import PathLike
-    from typing import Self
 
     from numpy.typing import ArrayLike
 
@@ -263,7 +262,7 @@ def as_dict(self):
         return dct
 
     @classmethod
-    def from_dict(cls, dct) -> Self:
+    def from_dict(cls, dct) -> PhononBandStructure:
         """
         Args:
             dct (dict): Dict representation.
@@ -592,7 +591,7 @@ def as_dict(self) -> dict:
         return dct
 
     @classmethod
-    def from_dict(cls, dct: dict) -> Self:
+    def from_dict(cls, dct: dict) -> PhononBandStructureSymmLine:
         """
         Args:
             dct: Dict representation.
diff --git a/pymatgen/phonon/dos.py b/pymatgen/phonon/dos.py
index 14cbbaa1125..766afd9ad5d 100644
--- a/pymatgen/phonon/dos.py
+++ b/pymatgen/phonon/dos.py
@@ -14,7 +14,6 @@
 
 if TYPE_CHECKING:
     from collections.abc import Sequence
-    from typing import Self
 
 BOLTZ_THZ_PER_K = const.value("Boltzmann constant in Hz/K") / const.tera  # Boltzmann constant in THz/K
 THZ_TO_J = const.value("hertz-joule relationship") * const.tera
@@ -63,7 +62,7 @@ def get_smeared_densities(self, sigma: float) -> np.ndarray:
 
         return gaussian_filter1d(self.densities, sigma / avgdiff)
 
-    def __add__(self, other: Self) -> Self:
+    def __add__(self, other: PhononDos) -> PhononDos:
         """Adds two DOS together. Checks that frequency scales are the same.
         Otherwise, a ValueError is thrown.
 
@@ -78,7 +77,7 @@ def __add__(self, other: Self) -> Self:
         densities = self.densities + other.densities
         return PhononDos(self.frequencies, densities)
 
-    def __radd__(self, other: Self) -> Self:
+    def __radd__(self, other: PhononDos) -> PhononDos:
         """Reflected addition of two DOS objects.
 
         Args:
@@ -105,7 +104,7 @@ def __str__(self) -> str:
         return "\n".join(stringarray)
 
     @classmethod
-    def from_dict(cls, d: dict[str, Sequence]) -> Self:
+    def from_dict(cls, d: dict[str, Sequence]) -> PhononDos:
         """Returns PhononDos object from dict representation of PhononDos."""
         return cls(d["frequencies"], d["densities"])
 
@@ -344,7 +343,7 @@ def get_element_dos(self) -> dict:
         return {el: PhononDos(self.frequencies, densities) for el, densities in el_dos.items()}
 
     @classmethod
-    def from_dict(cls, dct: dict) -> Self:
+    def from_dict(cls, dct: dict) -> CompletePhononDos:
         """Returns CompleteDos object from dict representation."""
         tdos = PhononDos.from_dict(dct)
         struct = Structure.from_dict(dct["structure"])
diff --git a/pymatgen/phonon/ir_spectra.py b/pymatgen/phonon/ir_spectra.py
index 4827c933d51..b583dfbf7f6 100644
--- a/pymatgen/phonon/ir_spectra.py
+++ b/pymatgen/phonon/ir_spectra.py
@@ -19,7 +19,6 @@
 if TYPE_CHECKING:
     from collections.abc import Sequence
     from os import PathLike
-    from typing import Self
 
     from matplotlib.axes import Axes
     from numpy.typing import ArrayLike
@@ -59,7 +58,7 @@ def __init__(
         self.epsilon_infinity = np.array(epsilon_infinity)
 
     @classmethod
-    def from_dict(cls, dct: dict) -> Self:
+    def from_dict(cls, dct: dict) -> IRDielectricTensor:
         """Returns IRDielectricTensor from dict representation."""
         structure = Structure.from_dict(dct["structure"])
         oscillator_strength = dct["oscillator_strength"]
diff --git a/pymatgen/phonon/thermal_displacements.py b/pymatgen/phonon/thermal_displacements.py
index d69e784710e..ff434ffbd81 100644
--- a/pymatgen/phonon/thermal_displacements.py
+++ b/pymatgen/phonon/thermal_displacements.py
@@ -17,7 +17,6 @@
 
 if TYPE_CHECKING:
     from os import PathLike
-    from typing import Self
 
     from numpy.typing import ArrayLike
 
@@ -250,7 +249,9 @@ def _angle_dot(a: ArrayLike, b: ArrayLike) -> float:
         description="Angle: A new tool for validating theoretically derived anisotropic displacement "
         "parameters with experiment.",
     )
-    def compute_directionality_quality_criterion(self, other: Self) -> list:
+    def compute_directionality_quality_criterion(
+        self, other: ThermalDisplacementMatrices
+    ) -> list[dict[str, ArrayLike]]:
         """Will compute directionality of prolate displacement ellipsoids as described in
         https://doi.org/10.1039/C9CE00794F with the earlier implementation: https://github.com/damMroz/Angle/.