forte2.dsrg.dsrg_mrpt2
======================

.. py:module:: forte2.dsrg.dsrg_mrpt2




Module Contents
---------------

.. py:class:: DSRG_MRPT2

   Bases: :py:obj:`forte2.dsrg.dsrg_base.DSRGBase`


   
   Spin-adapted driven similarity renormalization group
   second-order multireference perturbation theory (DSRG-MRPT2).


   :Parameters:

       **flow_param** : float, optional, default=0.5
           The flow parameter (in atomic units) that controls the renormalization.

       **relax_reference** : int | str | bool, optional, default=False
           Relax the CI reference in response to dynamical correlation.
           If an integer is given, it specifies the maximum number of relaxation iterations.
           If a string is given, it must be one of 'once', 'twice', or 'iterate':
               'once' : diagonalize the CI Hamiltonian once after computing the DSRG energy
               'twice': after the first diagonalization, recompute the DSRG energy
               'iterate': keep relaxing until convergence or reaching relax_maxiter.
           If a boolean is given, True is equivalent to relax_maxiter and False means no relaxation.

       **relax_maxiter** : int, optional, default=10
           The maximum number of reference relaxation iterations.

       **relax_tol** : float, optional, default=1e-6
           The convergence tolerance for reference relaxation (in Hartree).

   :Attributes:

       **E_dsrg** : float
           The DSRG-MRPT2 total energy evaluated with the current reference.

       **E_relaxed_ref** : float
           The DSRG-MRPT2 total energy after reference relaxation.

       **relax_energies** : NDArray
           The history of DSRG-MRPT2 total energies during reference relaxation.
           Given as [[Edsrg(fixed_reference), Edsrg(relaxed_reference), Eref], ...].

       **relax_eigvals** : np.ndarray
           The eigenvalues of the relaxed CI Hamiltonian.

       **relax_eigvals_history** : NDArray
           The history of eigenvalues of the relaxed CI Hamiltonian during relaxation.











   .. rubric:: References

   .. [Rc11f4ed58ecb-1] F. A. Evangelista, "A driven similarity renormalization group approach to quantum many-body problems",
          J. Chem. Phys. 2014, 141, 054109.
   .. [Rc11f4ed58ecb-2] C. Li and F. A. Evangelista, "Multireference driven similarity renormalization group: A second-order perturbative analysis",
          J. Chem. Theory Comput. 2015, 11, 2097-2108.
   .. [Rc11f4ed58ecb-3] K. P. Hannon, C. Li, and F. A. Evangelista, "An integral-factorized implementation of the driven similarity renormalization group second-order multireference perturbation theory",
             J. Chem. Phys. 2016, 144, 204111.
   .. [Rc11f4ed58ecb-4] C. Li and F. A. Evangelista, "Driven similarity renormalization group for excited states: A state-averaged perturbation theory",
          J. Chem. Phys. 2018, 148, 124106.

   .. only:: latex

      [Rc11f4ed58ecb-1]_, [Rc11f4ed58ecb-2]_, [Rc11f4ed58ecb-3]_, [Rc11f4ed58ecb-4]_


   ..
       !! processed by numpydoc !!

   .. py:method:: get_integrals()


   .. py:method:: solve_dsrg(form_hbar=False)


   .. py:method:: do_reference_relaxation()