diff --git a/notebook/index.ipynb b/notebook/index.ipynb
index ebeac69..69c69a9 100644
--- a/notebook/index.ipynb
+++ b/notebook/index.ipynb
@@ -8,18 +8,25 @@
     "\n",
     "<hr style=\"height:1px;border:none;color:#cccccc;background-color:#cccccc;\" />\n",
     "\n",
+    "## Section 1: Numerical solution for 1D Schrödinger equation\n",
+    "\n",
     "<ol style=\"font-size:18px\">\n",
     "    <li><a href=\"./1quantumwell.ipynb\">Numerical Solution of the Schrödinger Equation for 1D Quantum Well</a></li>\n",
     "    <li><a href=\"./2quantumwells.ipynb\">Numerical Solution of the Schrödinger Equation for Two 1D Quantum Wells</a></li>\n",
     "    <li><a href=\"./asymmetricwell.ipynb\">Avoided Crossing in 1D Asymmetric Quantum Well</a></li>\n",
     "    <li><a href=\"./shooting_method.ipynb\">Shooting Method with Numerov Algorithm to Solve the Time Independent Schrödinger Equation for 1D Quantum Well</a></li>\n",
     "    <li><a href=\"./soft_intro.ipynb\">Numerical Solution of 1D Time Dependent Schrödinger Equation by Split Operator Fourier Transform (SOFT) Method</a></li>\n",
-    "    <li><a href=\"./ising_model.ipynb\">Ising Model in 2D</a></li>\n",
-    "    <li><a href=\"./pseudopotential.ipynb\">Pseudopotential</a></li>\n",
-    "    <li><a href=\"./verlet_2body.ipynb\">Verlet Algorithm</a></li>\n",
-    "    <li><a href=\"./brillouin_zone.ipynb\">Reciprocal space and Brillouin zone</a></li>\n",
-    "    <li><a href=\"./density_of_states.ipynb\">Density of States (DOS)</a></li>\n",
-    "    <li><a href=\"./free_electron.ipynb\">Free-electron bands in a periodic lattice</a></li>\n",
+    "</ol>"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Section 2: Band Theory of Crystals\n",
+    "\n",
+    "<ol style=\"font-size:18px\">\n",
+    "    <li><a href=\"./pseudopotential.ipynb\">Norm-conserving Pseudopotentials</a></li>\n",
     "</ol>"
    ]
   },