.. _input_description_co:

:orphan:

CO molecule example
===================

By using a carbon monoxide (CO) in a small rectangular box as an example, short description on the input variables is provided here.

``nfinp_scf``::

  WF_OPT    DAV
  NTYP      2
  NATM      2
  GMAX      5.50
  GMAXP     20.00
  NSCF      200
  MIX_ALPHA 0.8
  WIDTH     0.0010
  EDELTA    1.D-10
  NEG       8
  CELL      6.00  4.00  4.00  90.00  90.00  90.00
  CPUMAX    1700
  &ATOMIC_SPECIES
   C  12.011  pot.C_pbe1
   O  15.999  pot.O_pbe1
  &END
  &ATOMIC_COORDINATES
    0.0000  0.0000  0.0000  1  1  1
    2.2000  0.0000  0.0000  1  1  2
  &END

Each input variables and blocks (&[BLOCK_NAME] ... &) are explained below:

.. code:: bash

  WF_OPT    DAV

``WF_OPT`` is used to specify the wave function method. Default is ``DAV``.

.. code:: bash

  NTYP      2

``NTYP`` defines the number of atomic species in the system.

.. code:: bash

  NATM      2

``NATM`` defines the number of atoms in the unit cell.

.. code:: bash

  GMAX      5.50

``GMAX`` is the cutoff wave vector for the plane wave expansion of the wave functions. GMAX**2 corresponds to the cutoff energy in Rydberg.

.. code:: bash

  GMAXP     20.00

``GMAXP`` is the cutoff wave vector for the plane wave expansion of charge density. GMAXP**2 corresponds to the cutoff energy in Rydberg.

.. code:: bash

  NSCF      200

``NSCF`` is the maximum number of iteration for the wave function optimization [self-consistent field (SCF)]. Default is 200.

.. code:: bash

  MIX_ALPHA 0.8

``MIX_ALPHA`` is the mixing parameter for the charge density mixing. Default is 0.7.

.. code:: bash

  WIDTH     0.0010

``WIDTH`` is the width of the broadening to approximate the delta function in Hartree. For systems with a gap, very small positive ``WIDTT`` is used. In such a case, it does not have a physical meaning and is used to determine the Fermi level.

.. code:: bash

  EDELTA    1.D-10

``EDELTA`` is the convergence threshold for the total energy in Hartree per atom for the SCF calculation.

.. code:: bash

  NEG       8

``NEG`` is the number of states/bands considered in the calculation. STATE does not allow an occupied-state only calculation, and therefore ``NEG`` should be large enough to include occupied states and some unoccupied states.

.. code:: bash

  CELL      6.00  4.00  4.00  90.00  90.00  90.00

``CELL`` defines the cell parameter :math:`a`, :math:`b`, :math:`c`, :math:`\alpha`, :math:`\beta`, and :math:`\gamma`, where :math:`a`, :math:`b`, :math:`c`, are the lengths (in Bohr) of the 1st, 2nd, and 3rd lattice vectors, respectively, and :math:`\alpha`, :math:`\beta`, and :math:`\gamma`, are the angles (in degree) between 2nd and 3rd, 3rd and 1st, and 1st and 2nd lattice vectors, respectively.

.. code:: bash

  CPUMAX    1700

``CPUMAX`` is used to set the maximum time (in second) to terminate the execution of ``STATE`` (safely) before the maximum computational hours defined by the system, and restart the calculation.

.. note::
	``CPUMAX`` should be set smaller than the maximum time defined in the job script and the computational system. In this example, the maximum time set in the job script is 30 minutes and therefore ``CPUMAX`` should be slightly smaller than 30 * 60 = 1800.

.. code:: bash

  &ATOMIC_SPECIES
   C  12.011  pot.C_pbe1
   O  15.999  pot.O_pbe1
  &END

The block ``&ATOMIC_SPECIES ... &END`` is used to define the atomic types. The syntax is similar to the one in Quantum-ESPRESSO.

 Syntax::

        &ATOMIC_SPECIES
         ATOMIC_NUMBER(1) ATOMIC_MASS(1) PSEUDOPOTENTIAL_FILE(1) 
         ATOMIC_NUMBER(2) ATOMIC_MASS(2) PSEUDOPOTENTIAL_FILE(2) 
         ...
         ATOMIC_NUMBER(NTYP) ATOMIC_MASS(NTYP) PSEUDOPOTENTIAL_FILE(NTYP) 
        &END

 or::

        &ATOMIC_SPECIES
         ATOMIC_SYMBOL(1) ATOMIC_MASS(1) PSEUDOPOTENTIAL_FILE(1) 
         ATOMIC_SYMBOL(2) ATOMIC_MASS(2) PSEUDOPOTENTIAL_FILE(2)
         ...
         ATOMIC_SYMBOL(NTYP) ATOMIC_MASS(NTYP) PSEUDOPOTENTIAL_FILE(NTYP) 
        &END
 
 where ``NTYP`` is the number of atomic species.

.. code:: bash

  &ATOMIC_COORDINATES
    0.0000  0.0000  0.0000  1  1  1
    2.2000  0.0000  0.0000  1  1  2
  &END

The block ``&ATOMIC_COORDINATES ... &END`` is used to define the atomic coordinates in the legacy STATE format.

 Syntax::

        &ATOMIC_COORDINATES [CRYSTAL|CRYS|CARTESIAN|CART]
         CPS(1,1) CPS(1,2) CPS(1,3) IWEI(1) IMDTYP(1) ITYP(1)
         CPS(2,1) CPS(2,2) CPS(2,3) IWEI(2) IMDTYP(2) ITYP(2)
         ...
         CPS(NATM,1) CPS(NATM,2) CPS(NATM,3) IWEI(NATM) IMDTYP(NATM) ITYP(NATM)
        &END
        

 ``CARTESIAN``/``CART``: If set, atomic coordinates are given in the cartesian coordinate

 ``CRYSTAL``/``CRYS``: If set, atomic coordinates are given in the crystal coordinate

 ``CPS``: Atomic coordinate in the cartesian (``NCORD=1`` or ``COORD=CARTESIAN``) or in the crystal (``NCORD=0`` or ``COORD=CRYSTAL``) coordinate

 ``IWEI``: number of equivalent atoms under the inversion symmetry (currently inversion symmetry is disabled and always ``IWEI`` is always set to 1).

 ``IMDTYP``:

 * 1: Allow to move the ion

 * 0: Fix the ion

 Default coordinate system is ``CARTESIAN``. This is chosen when ``&ATOMIC_COORDINATES`` without argument is used.