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      "source": [
        "\n\n# Equation of state (EOS)\n\nFirst, do a bulk calculation for different lattice constants:\n"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": null,
      "metadata": {
        "collapsed": false
      },
      "outputs": [],
      "source": [
        "import numpy as np\n\nfrom ase import Atoms\nfrom ase.calculators.emt import EMT\nfrom ase.eos import EquationOfState\nfrom ase.io import read\nfrom ase.io.trajectory import Trajectory\nfrom ase.units import kJ\n\na = 4.0  # approximate lattice constant\nb = a / 2\nag = Atoms(\n    'Ag', cell=[(0, b, b), (b, 0, b), (b, b, 0)], pbc=1, calculator=EMT()\n)  # use EMT potential\ncell = ag.get_cell()\ntraj = Trajectory('Ag.traj', 'w')\nfor x in np.linspace(0.95, 1.05, 5):\n    ag.set_cell(cell * x, scale_atoms=True)\n    ag.get_potential_energy()\n    traj.write(ag)"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {},
      "source": [
        "This writes a trajectory file containing five configurations of FCC silver\nfor five different lattice constants. Now, analyse the result with\nthe :class:`~ase.eos.EquationOfState` class:\n\n"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": null,
      "metadata": {
        "collapsed": false
      },
      "outputs": [],
      "source": [
        "configs = read('Ag.traj@0:5')  # read 5 configurations\n# Extract volumes and energies:\nvolumes = [ag.get_volume() for ag in configs]\nenergies = [ag.get_potential_energy() for ag in configs]\neos = EquationOfState(volumes, energies)\nv0, e0, B = eos.fit()\nprint(B / kJ * 1.0e24, 'GPa')\neos.plot('Ag-eos.png')"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {},
      "source": [
        "A quicker way to do this analysis is to use the :mod:`ase.gui` tool::\n\n    $   ase gui Ag.traj\n\n"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {},
      "source": [
        "And then choose :menuselection:`Tools --> Bulk modulus`.\n\n"
      ]
    }
  ],
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