Modify a system#

For fixed ion positions, one finds the electronic ground state by varying the density to minimize the total energy.

`minimize_energy`	Minimize total energy with LBFGS algorithm.
`minimize_energy_tpsd`	Minimize total energy with two-point steepest descent algorithm.

Other common modifications include moving the ions or changing the simulation box.

`move_ions`	Move the ions to new coordinates, keeping the box fixed.
`set_box`	Set the simulation box size and shape by changing the box vectors.

Some uncommon modifications are useful for testing purposes.