chore: small adjustments

Author: VsevolodX

other/materials_designer/Introduction.ipynb

@@ -35,7 +35,7 @@
     "\n",
     "#### [1.6. Slab Perturbation](create_perturbation.ipynb)\n",
     "\n",
-    "This notebook lets user create a slab and perturb it by moving atoms according to a specified function. [Click here to open the notebook](create_perturbation.ipynb).\n",
+    "This notebook lets user add a perturbation to a slab by moving atoms according to a specified function. [Click here to open the notebook](create_perturbation.ipynb).\n",
     "\n",
     "### 2. Data Import\n",
     "\n",

other/materials_designer/create_perturbation.ipynb

@@ -5,7 +5,7 @@
    "source": [
     "# Create a Perturbation in a Material\n",
     "\n",
-    "Create a perturbation in a material with a specified smooth function. \n",
+    "Create a perturbation in a material with a specified smooth function or a custom function described with [SymPy](https://docs.sympy.org/latest/tutorials/intro-tutorial/intro.html) expressions. \n",
     "\n",
     "<h2 style=\"color:green\">Usage</h2>\n",
     "\n",
@@ -34,7 +34,7 @@
    "cell_type": "markdown",
    "source": [
     "## 1. Prepare the Environment\n",
-    "### 1.1. Set up defect parameters "
+    "### 1.1. Set up supercell parameters "
    ],
    "metadata": {
     "collapsed": false
@@ -127,7 +127,7 @@
     "from utils.visualize import visualize_materials as visualize\n",
     "from mat3ra.made.tools.build.supercell import create_supercell\n",
     "\n",
-    "unit_cell = materials[1]\n",
+    "unit_cell = materials[0]\n",
     "supercell = create_supercell(unit_cell, supercell_matrix=SUPERCELL_MATRIX)\n",
     "visualize(supercell, repetitions=[1, 1, 1], rotation=\"0x\")"
    ],
@@ -248,8 +248,7 @@
     "from mat3ra.made.tools.build.perturbation import CellMatchingDistancePreservingSlabPerturbationBuilder\n",
     "from mat3ra.made.tools.utils.perturbation import PerturbationFunctionHolder\n",
     "\n",
-    "x = sp.Symbol(\"x\")\n",
-    "y = sp.Symbol(\"y\")\n",
+    "x,y = sp.symbols('x y')\n",
     "function = amplitude * sp.sin(2 * sp.pi * x / wavelength + phase) * sp.sin(2 * sp.pi * y / wavelength)\n",
     "\n",
     "custom_perturbation_function = PerturbationFunctionHolder(function=function, variables=[\"x\", \"y\"])\n",