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112 lines
4.8 KiB
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112 lines
4.8 KiB
ReStructuredText
=======================
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Programming in the |qp|
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=======================
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To program in the |qp|, it is required that you are familiar with the |IRPF90|
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code generator. A GitBook can be found `here <http://scemama.gitbooks.io/irpf90>`_,
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and programmers are encouraged to visit this manual.
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|IRPF90| makes programming very simple. The only information a programmer needs
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in order to write a new program is the name of the required |IRPF90| entities
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which may already exist in other modules. For example, writing a program which
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prints the Hartree-Fock energy is as simple as:
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.. code:: fortran
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program print_hf_energy
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implicit none
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BEGIN_DOC
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! Program which prints the Hartree-Fock energy
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! to the standard output
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END_DOC
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print *, 'HF energy = ', HF_energy
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end
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The only required information was the existence of a provider for
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:command:`HF_energy`. A detailed list of all the providers, subroutines
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and functions of the |qp| can be found in the appendix of this manual.
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Architecture
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============
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As |IRPF90| is used, the programmer doesn't have full control of the sequence
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of instructions in the produced Fortran code. This explains why the input data
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is stored in a database rather than in sequential text files. Consequently, the
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programmer can't know in advance the order in which the files will be read, so a
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simple random access to persistent data is needed. The |EZFIO| library generator
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is a practical answer to this problem.
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The |qp| uses a collection of programs inter-operating together. Each of these
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programs is reading and/or modifying information in the |EZFIO| database.
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This is done mostly using the command line or scripting.
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.. important::
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Each command modifies the state of the |EZFIO| database, so running the
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same program twice on the same database may have different behavior because of the
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state of the database. For reproducibility, users are encouraged to run scripts
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where a fresh new |EZFIO| database is created at the beginning of the
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script. This way of running the |qp| makes calculations reproducible.
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The computational part |qp| is organized in **modules**. A module is a
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directory which contains multiple |IRPF90| files, a |README| and a |NEED| file.
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The |README| file contains documentation about the module, that is
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automatically included in the documentation of the |qp|. The documentation is
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generated by the `Sphinx documentation builder <http://www.sphinx-doc.org>`_,
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and it should be written using the |rst| format.
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The |NEED| file contains the list of the modules which are needed for the
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current module. When a module is needed, it means that all the |IRPF90| files
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it contains should be included in the current module. This is done
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automatically during the building process, by creating symbolic links in the
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current directory.
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To compile the program, the |Ninja| build system is used, and all the building
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process is fully automated such that the programmer will never have to modify a
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file by hand. Running :command:`ninja` inside a module will compile only the
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module, and running :command:`ninja` at the root of the |qp| will build all the
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modules, as well as the tools.
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Algorithms
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==========
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The `PhD thesis of Yann Garniron <https://doi.org/10.5281/zenodo.2558127>`_
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gives all the details about the implementation of:
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* The data structure for the two-electron integrals (:file:`utils/map_module.f`)
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* The Davdison diagonalization (module :ref:`module_davidson`)
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* The CIPSI selection (module :ref:`module_cipsi`)
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* The hybrid stochastic/deterministic PT2 correction (module :ref:`module_cipsi`)
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* The hybrid stochastic/deterministic matrix dressing (module :ref:`module_dressing`)
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Extracting results for use with other codes
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===========================================
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The |AOs| and |MOs| can be seen with :ref:`qp_edit`. We also provide a utility
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to create a file which can be read by `molden` for visualizing the |MOs| (see
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:ref:`molden`). For using external |CI| solvers, we provide a utility that
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generates a file containing the two-electron integrals in the |MO| basis set
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in the `FCIDUMP` format (see :ref:`fcidump`).
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All the results are stored in the |EZFIO| directory, so users willing to fetch
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data such as the |MOs| or the |CI| coefficients should use the |EZFIO| API.
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There are multiple major ways to do this:
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* Write a script in Python or OCaml and use the Python |EZFIO| API. The script
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:file:`$QP_ROOT/bin/qp_convert_output_to_ezfio` is a good example to understand
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how to use the |EZFIO| API in Python,
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* Write an independent program in Fortran or C, link it with the |EZFIO| library
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located at :file:`$QP_ROOT/external/ezfio/lib/libezfio.a` and call directly
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the |EZFIO| routines,
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* Write a new module for the |qp| printing the desired quantities in a suitable
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text format. The program :ref:`fcidump` is an example of such a program.
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