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ao_two_e_ints
==================
Here, all two-electron integrals (:math:`1/r_{12}`) are computed.
As they have 4 indices and many are zero, they are stored in a map, as defined
in :file:`utils/map_module.f90`.
To fetch an |AO| integral, use the
`get_ao_two_e_integral(i,j,k,l,ao_integrals_map)` function.
The conventions are:
* For |AO| integrals : (ij|kl) = (11|22) = = <12|12>