The XYZ file format consists of two header lines, the first of which contains the number of atoms, and the second of which is a title. The remaining lines each specify the coordinates of one atom, with the chemical symbol in the first field, and the , , coordinates following. A sequence number may be appended to the chemical symbol; it is then interpreted as the atomic group number, which can be used when different basis sets are wanted for different atoms of the same kind. The basis set is then specified for this group number rather than the atomic symbol. As a further extension, the first two header lines can be omitted.
Note that for XYZ input the default is not to reorient the molecule. Orientation can be forced, however, by the MASS or CHARGE options on the ORIENT directive.
The XYZ format had been specified within the documentation distributed with the Minnesota Supercomputer Center's XMol package. Note that MOLPRO has the facility to write XYZ files with the PUT command (see section 10.3).email@example.com 2018-12-09