AN AB-INITIO TREATMENT OF THE ELECTRONIC ABSORPTION-SPECTRA OF EXCESS-ELECTRON ALKALI-HALIDE CLUSTERS NAN+1CLN UP TO NA18CL17

Electronic excitation energies of alkali-excess clusters Na2Cl, Na3Cl2 , Na4Cl3, Na6Cl5, Na14Cl13, and Na18C17, are investigated using CIS (c onfiguration interaction singles) and RPA (random phase approximation) . The accuracy of these approximations is established for Na2Cl by equ ation-of-motion coupled-cluster singles and doubles calculations and b y comparison to experimental results. The mode of localization of the excess electron is decisive for the electronic excitation energy. No c luster-size dependence of the excitation energy is found. The direct U HF-CIS (unrestricted Hartree-Fock-CIS) and UHF-RPA implementation with in the program package TURBOMOLE is briefly described in the appendix. (C) 1995 American Institute of Physics.