mirror of
https://github.com/QuantumPackage/qp2.git
synced 2024-12-27 13:53:29 +01:00
80 lines
2.2 KiB
ReStructuredText
80 lines
2.2 KiB
ReStructuredText
.. _cisd:
|
||
|
||
.. program:: cisd
|
||
|
||
====
|
||
cisd
|
||
====
|
||
|
||
|
||
|
||
|
||
Configuration Interaction with Single and Double excitations.
|
||
|
||
This program takes a reference Slater determinant of ROHF-like occupancy,
|
||
|
||
and performs all single and double excitations on top of it, disregarding
|
||
spatial symmetry and compute the "n_states" lowest eigenstates of that CI
|
||
matrix (see :option:`determinants n_states`).
|
||
|
||
This program can be useful in many cases:
|
||
|
||
* **Ground state calculation**: if even after a :c:func:`cis` calculation, natural
|
||
orbitals (see :c:func:`save_natorb`) and then :c:func:`scf` optimization, you are not sure to have the lowest scf
|
||
solution,
|
||
do the same strategy with the :c:func:`cisd` executable instead of the :c:func:`cis` exectuable to generate the natural
|
||
orbitals as a guess for the :c:func:`scf`.
|
||
|
||
|
||
|
||
* **Excited states calculations**: the lowest excited states are much likely to
|
||
be dominanted by single- or double-excitations.
|
||
Therefore, running a :c:func:`cisd` will save the "n_states" lowest states within
|
||
the CISD space
|
||
in the |EZFIO| directory, which can afterward be used as guess wave functions
|
||
for a further multi-state fci calculation if you specify "read_wf" = True
|
||
before running the fci executable (see :option:`determinants read_wf`).
|
||
Also, if you specify "s2_eig" = True, the cisd will only retain states
|
||
having the good value :math:`S^2` value
|
||
(see :option:`determinants expected_s2` and :option:`determinants s2_eig`).
|
||
If "s2_eig" = False, it will take the lowest n_states, whatever
|
||
multiplicity they are.
|
||
|
||
|
||
|
||
Note: if you would like to discard some orbitals, use
|
||
:ref:`qp_set_mo_class` to specify:
|
||
|
||
* "core" orbitals which will be always doubly occupied
|
||
|
||
* "act" orbitals where an electron can be either excited from or to
|
||
|
||
* "del" orbitals which will be never occupied
|
||
|
||
|
||
Needs:
|
||
|
||
.. hlist::
|
||
:columns: 3
|
||
|
||
* :c:data:`read_wf`
|
||
|
||
Calls:
|
||
|
||
.. hlist::
|
||
:columns: 3
|
||
|
||
* :c:func:`run`
|
||
|
||
Touches:
|
||
|
||
.. hlist::
|
||
:columns: 3
|
||
|
||
* :c:data:`fock_matrix_ao_alpha`
|
||
* :c:data:`fock_matrix_ao_alpha`
|
||
* :c:data:`mo_coef`
|
||
* :c:data:`level_shift`
|
||
* :c:data:`mo_coef`
|
||
* :c:data:`read_wf`
|