Reference data are defined in normal MOPAC data sets.
Each dataset describes a single system, such as cesium in the ^{2}P
state, (an excited state), water (a molecule), NO (a radical), sodium
sulfate anion, [NaSO_{4}]^{-}, an anion, etc. The values
of all reference data, except geometric, are given on Line 3 of a MOPAC data
set. For geometric reference data, the reference values (bond lengths and
angles) are given in the Z-matrix.

Text on Line 3 is not used by MOPAC, but is used by PARAM.

<> | A geometric parameter is not to be used as a reference |

<text> | A geometric parameter is to be used as a reference |

D=n.nn |
The reference dipole moment is defined as n.nn |

DR=<text> |
The reference dipole source is given by the mnemonic <text> |

DWT=n.n |
The default reference dipole moment weight
is to be multiplied by n.n |

GR=<text> |
The reference geometry source is given by the mnemonic <text> |

GWT=n.n |
The default reference geometry weight is to
be multiplied by n.n |

H=n.nn |
The reference Heat of Formation is defined as
n.nn |

H=n.nn+<text> |
The reference Heat of Formation is defined as
n.nn relative to ,text> |

HR=<text> |
The reference Heat of Formation source is given by the mnemonic <text> |

HWT=n.n |
The default reference Heat of Formation
weight is to be multiplied by n.n |

I=n.nn |
The reference Ionization Potential is defined as
n.nn |

IR=<text> |
The reference Ionization Potential source is given by the mnemonic <text> |

IWT=n.n |
The default reference Ionization Potential
weight is to be multiplied by n.n |

ROOT=<text> |
A named electronic state is to be used |