forte2.dsrg.rel_dsrg_mrpt2

Module Contents

class forte2.dsrg.rel_dsrg_mrpt2.RelDSRG_MRPT2

Bases: forte2.dsrg.dsrg_base.DSRGBase

Two-component relativistic driven similarity renormalization group second-order multireference perturbation theory (2C-DSRG-MRPT2).

Parameters:

flow_paramfloat, optional, default=0.5

The flow parameter (in atomic units) that controls the renormalization.

relax_referenceint | 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_maxiterint, optional, default=10

The maximum number of reference relaxation iterations.

relax_tolfloat, optional, default=1e-6

The convergence tolerance for reference relaxation (in Hartree).

Attributes:

E_dsrgfloat

The DSRG-MRPT2 total energy evaluated with the current reference.

E_relaxed_reffloat

The DSRG-MRPT2 total energy after reference relaxation.

relax_energiesNDArray

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

relax_eigvalsnp.ndarray

The eigenvalues of the relaxed CI Hamiltonian.

relax_eigvals_historyNDArray

The history of eigenvalues of the relaxed CI Hamiltonian during relaxation.

References

[1]

F. A. Evangelista, “A driven similarity renormalization group approach to quantum many-body problems”, J. Chem. Phys. 2014, 141, 054109.

[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.

[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.

[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.

get_integrals()

solve_dsrg(form_hbar=False)

do_reference_relaxation()