{
 "cells": [
  {
   "attachments": {},
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Variational Quantum Eigensolver\n",
    "\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "%pip install openfermionpyscf"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "-1.1371755939165522\n"
     ]
    }
   ],
   "source": [
    "import cudaq\n",
    "\n",
    "geometry = [('H', (0., 0., 0.)), ('H', (0., 0., .7474))]\n",
    "\n",
    "molecule, data = cudaq.chemistry.create_molecular_hamiltonian(\n",
    "    geometry, 'sto-3g', 1, 0)\n",
    "\n",
    "electron_count = data.n_electrons\n",
    "qubit_count = 2 * data.n_orbitals\n",
    "\n",
    "kernel, angles = cudaq.make_kernel(list)\n",
    "qubits = kernel.qalloc(qubit_count)\n",
    "\n",
    "# Prepare the Hartree Fock State.\n",
    "kernel.x(qubits[0])\n",
    "kernel.x(qubits[1])\n",
    "\n",
    "# Adds parameterized gates based on the UCCSD ansatz.\n",
    "cudaq.kernels.uccsd(kernel, qubits, angles, electron_count, qubit_count)\n",
    "\n",
    "parameter_count = cudaq.kernels.uccsd_num_parameters(electron_count,\n",
    "                                                     qubit_count)\n",
    "\n",
    "optimizer = cudaq.optimizers.COBYLA()\n",
    "\n",
    "energy, parameters = cudaq.vqe(kernel,\n",
    "                               molecule,\n",
    "                               optimizer,\n",
    "                               parameter_count=parameter_count)\n",
    "\n",
    "print(energy)"
   ]
  },
  {
   "attachments": {},
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "We see that the energy has converged to the ground state minimum as expected for $H_{2}$."
   ]
  }
 ],
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