:orphan:
.. _case_CmF:
===========================
Electronic structure of CmF
===========================
We want to investigate the structure of the diatomic molecule CmF (Curium Fluoride).
The curium atom
---------------
The ground state configuration of curium (Cm, Z=96) is :math:`[Rn]5f^76d^17s^2` (see `here `_ for general information
and `also here `_),
so with two open shells.
The number of microstates generated by this configuration is
.. math::
N_{det}=\left(\begin{array}{c}14\\7\end{array}\right)\left(\begin{array}{c}10\\1\end{array}\right)\left(\begin{array}{c}2\\2\end{array}\right) = 3432\times 10\times 1 = 34320
We first carry out an average-of-configuration Hartree-Fock calculation of the neutral atom.
A problem will be that by default DIRAC will order orbitals according to their energies and assume that inactive (fully occupied) orbitals
have lower energies than active (partly occupied) ones. This may not hold true for f elements, where the open :math:`(n-2)f` orbitals may have lower
energy than :math:`(n-1)d` and :math:`ns` orbitals. We shall therefore calculate the atom in two steps:
1. We calculate the trivalent cation :math:`Cm^{3+}` with electron configuration :math:`[Rn]5f^7`.
2. Once we have identified the :math:`6d` and :math:`7s` orbitals amongst the virtuals we can easily calculate the neutral atom using reordering of orbitals and overlap selection.
We shall next investigate the electronic structure of the diatomic CmF molecule. For ease of analysis we shall impose linear symmetry also in the atomic
calculation. We achieve this through the introduction of a ghost center
.. literalinclude:: Cm.xyz
The menu file for the trivalent cation then reads
.. literalinclude:: CmIII.inp
Note that
1. we perform Mulliken population on all positive-energy orbitals.
2. we use the keyword SHELL to only indicate atomic shell type since we do not need more detailed information
3. we specify that the ghost center has no basis.
We run the calculation using::
pam --inp=CmIII --mol=Cm.xyz --put "cf.CmIII=DFCOEF"
(keywords for parallel run omitted). Here is a snippet of the Mulliken population analysis
.. literalinclude:: CmIII.pop
One clearly sees that the fractionally occupied :math:`5f` orbitals are followed by first virtual :math:`7s`, then virtual :math:`6d` orbitals.
We want to reorder them as :math:`\left(5f,7s,6d\right)\rightarrow\left(5f,6d,7s\right)` such that both open shells follow the closed :math:`7s`
shell in the neutral atom. We therefore set up the input file
.. literalinclude:: Cm.inp
This assures that the orbitals are correctly ordered when we start the SCF iterations. In order to keep them in the desired order, we invoke
overlap selection. We impose non-dynamic overlap selection, which means that orbitals in a given iteration are selected based on their overlap
with the *initial* orbitals.