.. _phonopy_load_command:

phonopy-load command
====================

At phonopy v2.7.0, ``phonopy-load`` command is installed. This behaves
similarly to ``phonopy.load`` (:ref:`phonopy_load`) in the phonopy
python module. The main aim of introducing this command is to provide
uniform usage over many different force calculators. Once
``phonopy_disp.yaml`` is created, the following operations will be the
same using this command.

The following default behaviours are different from that of those
of ``phonopy`` command:

1. ``phonopy_xxx.yaml`` type file is always necessary in either of two
   ways:

   * ``phonopy_xxx.yaml`` type file is given as the first argument of
     the command.
   * ``phonopy_xxx.yaml`` type file is put in the current directory
     with one of the default filenames of ``phonopy_params.yaml``,
     ``phonopy_disp.yaml``,  ``phonopy.yaml``. The searching
     preference order is ``phonopy_params.yaml`` >
     ``phonopy_disp.yaml`` > ``phonopy.yaml``.

4. ``-c`` option (read crystal structure) does not exist.

5. Use of command options is recommended, but phonopy configuration
   file can be read through ``--config`` option.

6. If parameters for non-analytical term correction (NAC) are
   found, NAC is automatically enabled. This can be disabled by
   ``--nonac`` option.

7. When force constants are calculated from displacements and forces
   dataset, force constants are automatically symmetrized. To disable
   this, ``--no-sym-fc`` option is used.

8. ``--save-params`` option is added. With this option,
   ``phonopy_params.yaml`` that contains most of the information
   to run phonopy, i.e., crystal structure, displacement-force
   dataset, and non-analytical term correction parameters. When
   displacement-force dataset didn't exist, force constants are
   written.

Examples
--------

In the NaCl-qe example,

::

   % phonopy --qe -d --dim 2 2 2 --pa auto -c NaCl.in
   % phonopy-load -f NaCl-00{1,2}.out

With these commands, ``phonopy_disp.yaml`` and ``FORCE_SETS`` are
created. After this step, it is unnecessary to specify ``--qe`` option
to run with ``phonopy-load``. The following command works to draw band
structure.

::

   % phonopy-load --band auto -p

Data in ``FORCE_SETS`` and ``BORN`` can be saved in
``phonopy_params.yaml`` using ``--save-params`` option. Then phonons
can be calculated only with this file as fillows::

   % phonopy-load --save-params
   % mkdir test && cd test
   % mv ../phonopy_params.yaml .
   % phonopy-load --band auto -p

In the last line, ``phonopy_params.yaml`` is read without specifying
because this filename is researved name to be searched.