Basis Sets

Gaussian Type Orbitals (GTO) basis sets of both the pure/spherical and Cartesian kind can be used throughout most of the library. The internal ordering is consistent with libcint, but utility functions to convert between common alternative orderings, as well as between Cartesian and pure orbitals are available.

Basis set format

Basis sets are expected to be in json format, as provided by the basis set exchange

Basis sets directory

By default, occ will search the current path for a provided basis set name. Otherwise, it will search in the path specified by the OCC_BASIS_PATH environment variable.

NOTE: since the latest release the OCC_BASIS_PATH variable is now OCC_DATA_PATH.

Density fitting

Density fitting basis sets are available e.g. def2-universal-jkfit.