Document log(g f) cutoff option in TARDISAtomData (#273)

docs/quickstart.ipynb

@@ -12,7 +12,7 @@
     "\n",
     "**Note:**\n",
     "\n",
-    "Get familiar with the [Notation in Carsus](development/notation.rst) and learn how to correctly select ions.\n",
+    "Get familiar with the [Notation in Carsus](reference/notation.rst) and learn how to correctly select ions.\n",
     "    \n",
     "</div>"
    ]
@@ -268,6 +268,40 @@
     "You are done! Now you can use your file to run TARDIS simulations."
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "### Controlling the log(g f) Cutoff in TARDISAtomData\n",
+    "\n",
+    "By default, Carsus applies a cutoff of **log(g f) = -3** when processing spectral lines.  \n",
+    "This means transitions with log(g f) < -3 are excluded from the atomic data file.\n",
+    "\n",
+    "If you want to change this threshold, modify the `\"lines_loggf_threshold\"` value inside `levels_lines_param`:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "atom_data = TARDISAtomData(atomic_weights,\n",
+    "                           ionization_energies,\n",
+    "                           gfall_reader,\n",
+    "                           zeta_data,\n",
+    "                           chianti_reader,\n",
+    "                           cmfgen_reader,\n",
+    "                           levels_lines_param={\"lines_loggf_threshold\": -5})  # Example: Change cutoff to -5"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Setting lines_loggf_threshold to a lower value includes weaker transitions, while increasing it filters out more lines."
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},