Ab initio approach to the electronic properties of sodium-ammonia clusters: Comparison with ammonia clusters

Ab initio results for the electronic properties of sodium-ammonia [Na(NH3)(n);n=1-8] and the corresponding ionized structures [Na+(NH3)(n)] are reported and compared with those for neutral ammonia clusters [(NH3)(n)]. Emphasis was placed on the analysis of polarization effects and calculation of vertical and adiabatic ionization potentials. The theoretical discussion is based on second order Moller-Plesset perturbation theory and Green's function or electron propagator theory calculations. Our results for the ionization energies (IEs) of Na(NH3)(n) clusters are in very good agreement with experimental information. The relationship between the dependence of the IEs on the number of ammonia molecules (n), polarization effects, and hydrogen bond formation is investigated. The presence of a hydrogen bond acceptor-only ammonia molecule that binds a delocalized excess electron in Na(NH3)(6-7) clusters is discussed.