Modeling of photoabsorption spectra of small helium cluster cations through ab initio and semi-empirical approaches. A comparative study

Abstract

A comparative study has been performed to assess the reliability of a diatomics-in-molecules (DIM) representation of the potential energy surfaces in calculations of the photoabsorption spectra of selected charged helium clusters, He+N (N = 3, 4,10). Results of the computationally cheap DIM approach have been compared to data resulting from accurate ab initio methods (MRCI, EOM-CCSD) and extended basis sets (up to d-aug-cc-pVQZ). Both single-point calculations and averaged photoabsorption spectra calculations have been performed to observe the effect of approximations employed within the DIM approach. DIM predictions of photoabsorption spectra are in a fairly good agreement with the ab initio ones, which seems to indicate that the semi-empirical DIM approach is suitable for simulating larger ionic helium clusters for which more elaborate ab initio models are not practicable.