Ab initioeffective potentials for silicon

We report an effective potential (EP) for replacing the ten core electrons in calculations on the Si atom. This potential was obtained directly from ab initio calculations on the states of Si atom and no empirical data or adjustable parameters are used. These ab initio effective potentials are tested by carrying out Hartree-Fock, generalized-valence-bond, and extensive configuration-interaction calculations on various molecules. We considered Si, Si${\mathrm{H}}_3$, ${\mathrm{Si}}_2$, and ${\mathrm{H}}_3$Si${\mathrm{O}}_2$ and calculated excitation energies, ionization potentials, and electron affinities both using the EP and without the EP (ab initio). In essentially all cases the agreement is to better than 0.1 eV, providing strong evidence that the EP adequately represents the Si core.