If the $external_charges keyword is present, Q-Chem scans for a set of external charges to be incorporated into a calculation. The format is shown below and consists of Cartesian coordinates and the value of the point charge, with one charge per line. The charge is in atomic units and the coordinates are in Ångstroms, unless bohrs are selected by setting the $rem keyword INPUT_BOHR to TRUE. The external charges are rotated with the molecule into the standard nuclear orientation and are specified in the following format:
$external_charges x-coord1 y-coord1 z-coord1 charge1 x-coord2 y-coord2 z-coord2 charge2 x-coord3 y-coord3 z-coord3 charge3 $end
In addition, the user can request to add a charged cage around the molecule (for so-called “charge stabilization” calculations) using the keyword ADD_CHARGED_CAGE. See Section 7.8.7 for details.