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 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This notebook demonstrates how you can calculate reaction energies using the Materials API and pymatgen."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Caculated\n",
      "1.000 CaO + 1.000 CO2 -> 1.000 CaCO3\n",
      "Reaction energy = -145.39165028828774 kJ mol^-1\n",
      "Experimental\n",
      "1.000 CaO + 1.000 CO2 -> 1.000 CaCO3\n",
      "Reaction energy = -178.30000000000018 kJ mol^-1\n"
     ]
    }
   ],
   "source": [
    "from pymatgen.matproj.rest import MPRester\n",
    "from pymatgen import Composition\n",
    "from pymatgen.entries.computed_entries import ComputedEntry\n",
    "from pymatgen.core.units import FloatWithUnit\n",
    "from pymatgen.analysis.reaction_calculator import ComputedReaction\n",
    "\n",
    "#This initializes the REST adaptor. Put your own API key in if necessary.\n",
    "a = MPRester()\n",
    "\n",
    "#This gets all entries belonging to the Ca-C-O system.\n",
    "all_entries = a.get_entries_in_chemsys(['Ca', 'C', 'O'])\n",
    "\n",
    "#This method simply gets the lowest energy entry for all entry with the same composition.\n",
    "def get_most_stable_entry(formula):\n",
    "    relevant_entries = [entry for entry in all_entries if entry.composition.reduced_formula == Composition(formula).reduced_formula]\n",
    "    relevant_entries = sorted(relevant_entries, key=lambda e: e.energy_per_atom)\n",
    "    return relevant_entries[0]\n",
    "\n",
    "CaO = get_most_stable_entry(\"CaO\")\n",
    "CO2 = get_most_stable_entry(\"CO2\")\n",
    "CaCO3 = get_most_stable_entry(\"CaCO3\")\n",
    "\n",
    "reaction = ComputedReaction([CaO, CO2], [CaCO3])\n",
    "energy = FloatWithUnit(reaction.calculated_reaction_energy, \"eV atom^-1\")\n",
    "\n",
    "print(\"Caculated\")\n",
    "print(reaction)\n",
    "print(\"Reaction energy = {}\".format(energy.to(\"kJ mol^-1\")))\n",
    "print\n",
    "\n",
    "# The following portions demonstrate how to get the experimental values as well.\n",
    "exp_CaO = a.get_exp_entry(\"CaO\")\n",
    "exp_CaCO3 = a.get_exp_entry(\"CaCO3\")\n",
    "\n",
    "#Unfortunately, the Materials Project database does not have gas phase experimental entries. This is the value from NIST. We manually create the entry.\n",
    "#Exp entries should be in kJ/mol.\n",
    "exp_CO2 = ComputedEntry(\"CO2\", -393.51)\n",
    "\n",
    "exp_reaction = ComputedReaction([exp_CaO, exp_CO2], [exp_CaCO3])\n",
    "\n",
    "print(\"Experimental\")\n",
    "print(exp_reaction)\n",
    "print(\"Reaction energy = {} kJ mol^-1\".format(exp_reaction.calculated_reaction_energy))"
   ]
  }
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