Molpro 2012
===========

Molpro is a software package that allows for high level wavefunction-based quantum-chemistry and
is coupled to the :mod:`metafalcon` package by a text-based interface. Only CASSCF calculations have
been performed and tested so far to work with **metaFALCON**.

Molpro is used, if the following information is provided in the `meta-config.json` file under the
``"molecular dynamics"`` keyword::

    "interface": {
      "type": "molpro",
      "configure": {
        "nproc": 1
      }

It is possible to let Molpro run parallel calculations, if the ``"nproc"`` keyword is provided.

In order to allow the **metaFALCON** to construct the input textfile for Molpro in every
dynamics step, two additional files are needed. The file `head` contains everything that should
be in the Molpro input file before the molecular geometry. The file `tail`, on the other hand,
contains everything to be placed after the molecular geometry.

For example, if the `head` file is

::
    
    nosym;
    geometry={

and the `tail` file is

::

    }
    basis=6-31g
    {casscf
    closed,13
    occ,17
    wf,30,1,0;state,2;
    cpmcscf,grad,1.1,spin=0,record=5100.1
    cpmcscf,grad,2.1,spin=0,record=5101.1}
    force;samc,5100.1
    force;samc,5101.1

the **metaFALCON** will build a Molpro input file for the calculation of the first two excited \
state energies and gradients on the CASSCF level in every dynamics step.

.. note::
    In order to ensure that the active space does not change abruptly by the exchange of orbitals, a \
    temporary wavefunction file should be saved in each Molpro run. Therefore, the first line of the \
    `head` file should be::

        file,2,temp.wfu

    Note that an initial `temp.wfu` file has to be present before the start of the dynamics. \
    Now the `diab` directive can be used to guarantee that the active space is consistent with \
    the previous dynamics step. Insert the following lines into the `casscf` block after the `wf` \
    directive::
        
        orbital,2140.2
        diab,2140.2