========
ao_basis
========
This module describes the atomic orbitals basis set.
An |AO| :math:`\chi` centered on nucleus A is represented as:
.. math::
\chi_i({\bf r}) = (x-X_A)^a (y-Y_A)^b (z-Z_A)^c \sum_k c_{ki} e^{-\gamma_{ki} |{\bf r} - {\bf R}_A|^2}
The |AO| coefficients are normalized as:
.. math::
{\tilde c}_{ki} = \frac{c_{ki}}{ \int \left( (x-X_A)^a (y-Y_A)^b (z-Z_A)^c e^{-\gamma_{ki} |{\bf r} - {\bf R}_A|^2} \right)^2 dr}
Warning: `ao_coef` contains the |AO| coefficients given in input. These do not
include the normalization constant of the |AO|. The `ao_coef_normalized` provider includes
this normalization factor.
The |AOs| are also sorted by increasing exponent to accelerate the calculation of
the two electron integrals.