Changed the uhf value when xtb calculates with lanthanides

CHANGELOG.md

@@ -24,6 +24,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Breaking Changes
 - Removal of the `dist_threshold` flag and in the `-toml` file.
+- The number of unpaired electrons (`Molecule.uhf`) is now set to 0 if `xtb` is used as `QMMethod` and a lanthanide is within the molecule to match the `f-in-core` approximation.
 
 ## [0.4.0] - 2024-09-19
 ### Changed

src/mindlessgen/qm/xtb.py

@@ -6,9 +6,11 @@
 from pathlib import Path
 import shutil
 from tempfile import TemporaryDirectory
+import numpy as np
 from ..molecules import Molecule
 from .base import QMMethod
 from ..prog import XTBConfig
+from ..molecules.miscellaneous import get_lanthanides
 
 
 class XTB(QMMethod):
@@ -34,7 +36,24 @@ def optimize(
         """
         Optimize a molecule using xtb.
         """
-
+        if np.any(np.isin(molecule.ati, get_lanthanides())):
+            nel = 0
+            f_electrons = 0
+            for atom in molecule.ati:
+                nel += atom + 1
+                if atom in get_lanthanides():
+                    f_electrons += atom - 56
+            # Check if the number of the remaning electrons is even
+            test_rhf = nel - f_electrons - molecule.charge
+            if not test_rhf % 2 == 0:
+                raise SystemError(
+                    "Lanthanides detected, remaining number of electrons is not even."
+                )
+            # Store the original UHF value and set uhf to 0
+            # Justification: xTB does not treat f electrons explicitly.
+            # The remaining openshell system has to be removed.
+            uhf_original = molecule.uhf
+            molecule.uhf = 0
         # Create a unique temporary directory using TemporaryDirectory context manager
         with TemporaryDirectory(prefix="xtb_") as temp_dir:
             temp_path = Path(temp_dir).resolve()
@@ -71,13 +90,33 @@ def optimize(
             # read the optimized molecule
             optimized_molecule = molecule.copy()
             optimized_molecule.read_xyz_from_file(temp_path / "xtbopt.xyz")
-
+            if np.any(np.isin(molecule.ati, get_lanthanides())):
+                # Reset the UHF value to the original value before returning the optimized molecule.
+                optimized_molecule.uhf = uhf_original
             return optimized_molecule
 
     def singlepoint(self, molecule: Molecule, verbosity: int = 1) -> str:
         """
         Perform a single-point calculation using xtb.
         """
+        if np.any(np.isin(molecule.ati, get_lanthanides())):
+            nel = 0
+            f_electrons = 0
+            for atom in molecule.ati:
+                nel += atom + 1
+                if atom in get_lanthanides():
+                    f_electrons += atom - 56
+            # Check if the number of the remaning electrons is even
+            test_rhf = nel - f_electrons - molecule.charge
+            if not test_rhf % 2 == 0:
+                raise SystemError(
+                    "Lanthanides detected, remaining number of electrons is not even."
+                )
+            # Store the original UHF value and set uhf to 0
+            # Justification: xTB does not treat f electrons explicitly.
+            # The remaining openshell system has to be removed.
+            uhf_original = molecule.uhf
+            molecule.uhf = 0
 
         # Create a unique temporary directory using TemporaryDirectory context manager
         with TemporaryDirectory(prefix="xtb_") as temp_dir:
@@ -109,6 +148,8 @@ def singlepoint(self, molecule: Molecule, verbosity: int = 1) -> str:
                     f"xtb failed with return code {return_code}:\n{xtb_log_err}"
                 )
 
+            if np.any(np.isin(molecule.ati, get_lanthanides())):
+                molecule.uhf = uhf_original
             return xtb_log_out
 
     def check_gap(