mirror of
https://github.com/LCPQ/quantum_package
synced 2024-06-02 03:15:29 +02:00
42 lines
1.7 KiB
ReStructuredText
42 lines
1.7 KiB
ReStructuredText
.. _.cis.:
|
|
|
|
.. program:: cis
|
|
|
|
===
|
|
cis
|
|
===
|
|
|
|
|
|
|
|
|
|
Configuration Interaction with Single excitations.
|
|
|
|
This program takes a reference Slater determinant of ROHF-like occupancy, and performs all single excitations on top of it. Disregarding spatial symmetry, it computes 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
|
|
|
|
To be sure to have the lowest |SCF| solution, perform an :ref:`.scf.` (see the :ref:`hartree_fock` module), then a :ref:`.cis.`, save the natural orbitals (see :ref:`.save_natorb.`) and re-run an :ref:`.scf.` optimization from this |MO| guess.
|
|
|
|
|
|
|
|
# Excited states calculations
|
|
|
|
The lowest excited states are much likely to be dominated by single-excitations. Therefore, running a :ref:`.cis.` will save the `n_states` lowest states within the |CIS| space in the |EZFIO| directory, which can afterwards be used as guess wave functions for a further multi-state |FCI| calculation if :option:`determinants read_wf` is set to |true| before running the :ref:`.fci.` executable.
|
|
|
|
If :option:`determinants s2_eig` is set to |true|, the |CIS| will only retain states having the expected |S^2| value (see :option:`determinants expected_s2`). Otherwise, the |CIS| will take the lowest :option:`determinants n_states`, whatever multiplicity they are.
|
|
|
|
# Note
|
|
|
|
To discard some orbitals, use the :ref:`qp_set_mo_class` command 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
|
|
|
|
|
|
|
|
File: :file:`cis/cis.irp.f` |