The $QCAUX environment variable determines the directory where Q-Chem
searches for auxiliary files and the machine license. If not set explicitly,
it defaults to $QC/qcaux.
The $QCAUX directory contains files required to run Q-Chem
calculations, including basis set and ECP specifications, SAD
guesses (see Chapter 4),
library of standard effective fragments (see Section 12.5),
and instructions for the AOInts package for generating two-electron integrals efficiently.