To have a pictural illustration of the convergence of the |CIPSI| algorithm, just run
..code::
qp_e_conv_fci hcn.fci.out
This will create the files "hcn.fci.out.conv" containing the data of the convergence of the energy that can be plotted, together with the file "hcn.fci.out.conv.eps" which is obtained from the gnuplot plot file "hcn.fci.out.conv.plt".
These orbitals are in general known to be better than the usual |HF| |MOs| as they are obtained from a correlated wave function. To use these orbitals for future calculations, one has to replace the current |MOs| by the natural orbitals. To do so, just run:
..code::
qp_run save_natorb hcn
Hands on
========
..important::
As the |MOs| are changed, for the sake of coherence of future calculations, the save_natorb program
*automatically removes the current wave function* stored in the |EZFIO| database and replace
it by a single Slater determinant.
Then, you can run another |CIPSI| calculation to see how the use of natural orbital affect the convergence of the algorithm. For instance:
..code::
qp_run fci hcn | tee hcn.fci_natorb.out
and then
..code::
qp_e_conv_fci hcn.fci_natorb.out
Printing the near |FCI| wave function
-------------------------------------
Once obtained the near |FCI| energy, one can also take a closer look at the wave function stored in the |EZFIO| database.
If the wave function contains less than :math:`10^4` determinants, you can directly read it with the
:ref:`qp_edit` command. Just run
..code::
qp_edit hcn
..important::
The :ref:`qp_edit` mode virtually makes human-friendly the architecture of the |EZFIO| database
through *vim*-like editor.
Then, look for "hand" when you are in the :ref:`qp_edit` mode. If the research is negative,
then it means that the wave function stored in the |EZFIO| database is too large to be edited in :ref:`qp_edit` mode.
An alternative is to use the :command:`print_wf` command:
..code::
qp_run print_wf hcn | tee hcn.fci_natorb.wf
This program will, by default, print out the first :math:`10^4` determinants whatever the size of the wave function stored in the |EZFIO| folder. If you want to change the number of printed Slater determinants, just change the :option:`determinants n_det_print_wf` keyword using the :ref:`qp_edit` tool.