 
Summary: Ionization Energies of Linear and Cyclic Polysilanes.
Application of the Green's Function Method Coupled
with Semiempirical Molecular Orbital Calculations
Yitzhak Apeloig* and David Danovich
Department of Chemistry, TechnionIsrael Institute of Technology, Haifa 32000, Israel
Received July 26, 1995X
The ionization energies of the parent and permethylated linear [R3Si(SiR2)nSiR3] (n ) 13;
R ) H, CH3) and cyclic [(cSiR2)n] (n ) 36; R ) H, CH3) polysilanes have been calculated
with the outer valence Green's function (OVGF) technique, using as the zeroth order
approximation the wave functions obtained with semiempirical AM1, PM3, and MNDO
methods. It is found that the OVGF(AM1) method gives significantly better agreement with
the experimental ionization potentials than semiempirical calculations using Koopmans'
theorem. Furthermore, the OVGF(AM1) results are of comparable quality to those of OVA
and EPT ab initio calculations. The mean deviation, for all the studied molecules, between
the experimental and the OVGF(AM1) values is only 0.21 eV. The ionization energies of
the studied polysilanes behave as follows: (1) The first ionization energies of the permethy
lated polysilanes are significantly (by 11.7 eV) lower than those of the corresponding parent
polysilanes. (2) In the cyclic silanes the first IP is higher when the number of silicon atoms
in the polysilane increases, while in the openchain silanes the first IP decreases with the
number of silicon atoms. The crossover between the two series occurs between the Si4 and
