====== Exercise 2: Geometry optimization of the L-alanine crystal ======

To perform a geometry optimisation, we need to add a third main section to the input file. 

''MOTION'': contains all information related to structural changes during a calculation, such as geometry optimisation, cell optimisation, or molecular dynamics. 

The relevant input for geometry optimisation is:

<code>
&MOTION
  &GEO_OPT
    OPTIMIZER BFGS
    MAX_ITER 100
  &END GEO_OPT
&END MOTION
</code>

The subsection ''GEO_OPT'' controls how the geometry optimisation is carried out. Here, the keyword ''OPTIMIZER'' specifies the optimisation algorithm; in this example we use ''BFGS'', a quasi-Newton method that is efficient for molecular and solid-state systems. The keyword ''MAX_ITER'' sets the maximum number of optimisation steps (here 100). The optimisation will stop earlier if the convergence criteria are reached.

<note classic>
**Task:** Run the geometry optimisation of the L-alanine crystal. What do you have to do except adding the ''MOTION'' section? After the run, inspect the optimised structure using Mercury, VMD, VESTA, or another molecular visualisation program.
</note>