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   "source": [
    "# 14: Bonding In Crystals"
   ]
  },
  {
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   "metadata": {},
   "source": [
    "## Example number 1, Page number 361"
   ]
  },
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     "text": [
      "potential energy per ion pair is -3.981 eV\n",
      "answer in the book varies due to rounding off errors\n"
     ]
    }
   ],
   "source": [
    "#importing modules\n",
    "import math\n",
    "from __future__ import division\n",
    "\n",
    "#Variable declaration   \n",
    "e=1.6*10**-19;           #charge of electron(coulomb)\n",
    "r0=2.81*10**-10;             #distance between ions(m)\n",
    "A=1.748;      #constant\n",
    "x=9*10**9;         #let x=1/(4*math.pi*epsilon0)\n",
    "n=9;          \n",
    "\n",
    "#Calculations\n",
    "U0=-x*A*e**2*(1-(1/n))/(e*r0);       #potential energy per ion pair(eV)\n",
    "\n",
    "#Result\n",
    "print \"potential energy per ion pair is\",round(U0/2,3),\"eV\"\n",
    "print \"answer in the book varies due to rounding off errors\""
   ]
  }
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