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Construction of a Gaussian Basis Set

Basis functions are constructed using the CGBF (contracted Gaussian basis function) object, which, in turn, uses the PGBF (primitive Gaussian basis function) object. Basis sets are simply lists of CGBF's. In the Ints module there is a convenience function getbasis that constructs basis sets for different molecules. The syntax for the getbasis function is:

>>> bfs = getbasis(molecule,basis_data=None)

The basis data can be input from a number of data files in the PyQuante suite. Here are some of the more commonly used basis sets:
• basis_631ss The Pople 6-31G** basis set
• basis_sto3g The Pople STO-3G basis set
• basis_321 The Pople 3-21G basis set
• basis_ccpvtz The Dunning cc-pVTZ basis set
• basis_ccpvtzmf The Dunning cc-pVTZ(-f) basis set (cc-pVTZ without f-functions)
For, example, to construct a basis set for the h2o object for water created above, we would call

>>> from basis_631ss import basis_data
>>> bfs = getbasis(h2o,basis_data)

If the basis_data argument is omitted, the program will default to 6-31G**. As of version 1.6, you may now specify a string for the basis_data argument, e.g. "6-31G**" so you may do things like

>>> bfs = getbasis(h2o,'6-31G**')
>>> bfs2 = getbasis(h2o,'sto-3g')

and so on. Use PyQuante.Basis.Tools.basis_map.keys() for a list of the supported basis strings.