Default Grid Assesment

[Ali-Tehrani]

This pull-requests addresses Issue #179.
The Default rgrid was obtained from Horton. This corresponds to using the UniformInteger grid and PowerRTransform with a "fine" preset for the angular component. This is stored in grid/utils.py in a dictionary with the following:

r"""
Obtained from theochem/horton/data/grids/tv-13.5.txt with the folllowing preamble

These grids were created by Toon Verstraelen in July 2013 in a second effort
to generate tuned grids based on a series of diatomic benchmarks computed
with the QZVP basis of Ahlrichs and coworkers. They are constructed to give
on average 5 digits of precision for a variety of molecular integrals, using
the Becke scheme with k=3.
"""
# Items are (rmin, rmax, npts) in angstrom, Meant for PowerRTransform

If the user provided rgrid as None, then it generates the default radial grid.
The following functions and their tests (with two added) were changed to have default rgrid options:

• AtomGrid.from_preset
• MolGrid.from_preset
• MolGrid.from_size
• MolGrid.from_pruned

[Ali-Tehrani]

Added default BeckeWeights to aim_weights to all static, constructor methods

[FarnazH]

Thanks @Ali-Tehrani.

1. Shouldn't we make the rgrid in from_pruned method optional as well?
2. Thinking more after our discussion, I agree that we should remove *_ in arguments. It seems to have been used arbitrarily and as we are not using it anywhere else, it is best to remove it for now. Can you please remove them?

[Ali-Tehrani]

The *_ is removed.

If you're referring to AtomGrid.from_prune, default radial grid isn't added because atomic numbers is not included in its signature.

[FarnazH]

I removed * from the rest of AtomGrid class, which caused an API change (see cc61d59). If you have no further comments, feel free to merge this PR.

[marco-2023]

I did not find a way to add a commit to this PR. The only change that I would make is to substitute the values in line 198 of AtomGrid:

                rmin, rmax = rmin * 1.8897259885789, rmax * 1.8897259885789

by the corresponding scipy constants

                # convert angstrom to bohr
                ang2bohr = scipy.constants.angstrom / scipy.constants.value("atomic unit of length")
                rmin, rmax = rmin * ang2bohr, rmax * ang2bohr

just for consistency with the molgrid module.