Parameters for a particular atom include the resonance integrals, coulomb integral, valence, and symbol. The calculations can be performed using either a default set of parameters or user defined parameters. The default set of parameters are those suggested by Van-Catledge [J. Org. Chem.,1980,45,4801].
Parameters for a particular atom may altered by holding the command key down and choosing the desired atom from the palette. A window will appear containing the parameters defined for that atom; these parameters may then be altered as needed. Note that for certain elements (N, O ,P, and S) radio buttons are used to toggle between atoms that provide one electron to the π system (such as the N in pyridine) and those that provide two electrons (such as the N in pyrol). Three additional unspecified atoms (Xa, Xb, and Xc) are provided which may be defined by the user.
