.. _11_germanium_solid:

.. include:: ../../examples/11_germanium_solid/README.rst

----

.. code-block:: python

   import numpy as np
   
   from eminus import Atoms, SCF
   from eminus.units import ang2bohr, ev2ha
   

Create a germanium crystal with an FCC crystal structure

Here, :code:`a` is not only the unit cell size but the lattice constant as well, defining the periodicity

As a reminder, the :code:`center` option should not be used when explicitly using periodicity

Since electronvolt and Angstrom are common in solid-state physics convert the units here to atomic units

.. code-block:: python

   atom = "Ge8"
   a = ang2bohr(5.658)
   ecut = ev2ha(500)
   pos = a * np.array(
       [
           [0, 0, 0],
           [0, 0.5, 0.5],
           [0.25, 0.25, 0.25],
           [0.25, 0.75, 0.75],
           [0.5, 0, 0.5],
           [0.5, 0.5, 0],
           [0.75, 0.25, 0.25],
           [0.75, 0.75, 0.25],
       ]
   )
   atoms = Atoms(atom=atom, pos=pos, a=a, ecut=ecut)
   

Use the pseudopotential from Tomas Arias (only local and only for germanium)

The GTH pseudopotential will work as well and would include non-local effects

Reduce the convergence tolerance for this example

.. code-block:: python

   scf = SCF(atoms, pot="Ge", etol=1e-4)
   scf.run()
   

Save the density as a CUBE file

.. code-block:: python

   atoms.write("Ge_solid_density.cube", scf.n)
   

If you have the viewer extra installed, the following line will plot the unit cell and 20 isosurfaces of the density, such that 50% of the density is contained

.. code-block:: python

   # scf.view(plot_n=True, surfaces=20, percent=50)

Download :download:`11_germanium_solid.py <../../examples/11_germanium_solid/11_germanium_solid.py>`