THE DETERMINATION OF ELECTRON-AFFINITIES OF THE OPEN-SHELL SYSTEMS C AND CH2 USING THE MULTICONFIGURATIONAL SPIN TENSOR ELECTRON PROPAGATORMETHOD

The multiconfigurational spin tensor electron propagator method (MCSTE P) is a Green's function approach for accurately predicting and analyz ing ionization potentials (IPs) and electron affinities (EAs). Unlike more traditional Green's function approaches, MCSTEP is applicable to highly correlated and open shell systems as well as to closed shell sy stems with small correlation effects. We apply MCSTEP for the determin ation of EAs for C and CH2. This is the first time that MCSTEP has bee n used to determine the EAs for systems which have both open shell neu tral and anionic ground states. Our best MCSTEP results for the EA of C and the adiabatic EA of CH2 are 1.2904 and 0.6356 eV, respectively, compared to 1.2607 and 0.6306 eV, respectively, obtained with large sc ale multireference configuration interaction (MRCI) using the same bas is sets. Experimental values are 1.268 eV for C and 0.628+/-0.031 eV f or CH2. We also show that accurate EAs for these systems can be obtain ed both with MRCI and especially with MCSTEP using moderately sized ba sis sets composed of a good, standard core-valence basis set supplemen ted with some additional diffuse functions.