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132 lines
3.3 KiB
ReStructuredText
132 lines
3.3 KiB
ReStructuredText
=================
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Quick-start guide
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=================
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This tutorial should talk you through everything you need to get started with
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the |qp|. As an example, we will run a |CIPSI| calculation on the HCN molecule.
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Demo video
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==========
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.. Include demo video here
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Hands on
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========
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.. important::
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Before using the |qp|, it is required to source the file
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:file:`quantum_package.rc` if it has not been done already in the current
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shell.
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Create the EZFIO database
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-------------------------
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The data relative to calculations are stored in an |EZFIO| database.
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|EZFIO| is a hierarchical data format which uses the hierarchy of the file
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system to organize the data, as files stored in a directory.
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The data in the |EZFIO| directory are stored as plain text files, so it can be
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opened with any text editor.
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To access the data of the |EZFIO| database, the APIs (Fortran, |Python|,
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|OCaml| or Bash) provided by |EZFIO| should be used, or tools using these APIs
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such as :ref:`qp_edit` provided with the |qp|.
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First, create an `xyz` file containing the coordinates of the molecule.
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The file :file:`hcn.xyz` contains::
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3
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HCN molecule
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C 0.0 0.0 0.0
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H 0.0 0.0 1.064
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N 0.0 0.0 -1.156
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This xyz file is now used with the :ref:`qp_create_ezfio_from_xyz` command to
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create an |EZFIO| database with the 6-31G basis set:
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.. code:: bash
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qp_create_ezfio_from_xyz -b "6-31G" hcn.xyz -o hcn
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The EZFIO database now contains data relative to the nuclear coordinates and the atomic
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basis set:
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.. code:: bash
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$ ls hcn
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ao_basis/ electrons/ ezfio/ nuclei/ pseudo/
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Run a Hartree-Fock calculation
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------------------------------
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The program :ref:`qp_run` is the driver program of the |qp|. To run an SCF calculation,
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just run
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.. code:: bash
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qp_run scf hcn
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The expected energy is ``-92.827856698`` au.
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.. seealso::
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The documentation of the :ref:`hartree_fock` module.
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Choose the target |MO| space
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----------------------------
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Now, modify to |EZFIO| database to make |CIPSI| calculation in the
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full set of valence |MOs|, keeping the core |MOs| frozen. The simple
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command :command:`qp_set_frozen_core` does this automatically:
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.. code:: bash
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qp_set_frozen_core hcn
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Run the |CIPSI| calculation
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----------------------------
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We will now use the |CIPSI| algorithm to estimate the |FCI| energy.
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.. code::
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qp_run fci hcn
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The program will start with a single determinant and will iteratively:
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* Select the most important determinants from the external space and add them to the
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internal space
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* Add all the necessary determinants to allow the eigenvector of |H| to be
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also an eigenstate of |S^2|
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* Diagonalize |H| in the enlarged internal space
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* Compute (stochastically) the second-order perturbative contribution to the energy
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* Extrapolate the variational energy by fitting
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:math:`E=E_\text{FCI} - \alpha\, E_\text{PT2}`
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By default, the program will stop when more than one million determinants have
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entered in the internal space, or when the |PT2| energy is below :math:`10^{-4}`.
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The estimated |FCI| energy of HCN is ``-93.0501`` au.
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.. seealso::
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The documentation of the :ref:`fci` module.
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.. important:: TODO
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.. include:: /work.rst
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* Natural orbitals
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* Parameters for Hartree-Fock
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* Parameters for Davidson
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* Running in parallel
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* Parameters for selection (Generators/selectors)
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