Extended Hückel theory provides an all-valence-electron empirical approximation for solving the electronic Schrödinger equation. The Scigress ExtHückel application accepts a chemical sample file (*.csf) as input. The computation treats all valence electrons and calculates the electronic wavefunction of the structures in the chemical sample file. Double-zeta basis sets are used for d- and f- functions. Two parameter sets are provided, a standard set and the Alvarez collected set. You can use either of these parameter sets in Scigress, or implement others.
From the wavefunction, the electron density, molecular orbitals, electrostatic potential, partial charges, and bond orders are determined. Electronic information computed by the ExtHückel application is written to a file called huckel.out.
Electronic properties computed by the ExtHückel application can be displayed superimposed on the molecular structure from the chemical sample file.
Extended Hückel does not optimize the geometry; all properties are calculated on the current geometry.