Diatomics-in-molecules study of the geometric and electronic structure of Xe+ clusters

Photoabsorption spectra of small cationic xenon clusters from time-dependent density functional theory

“…Our results are summarized in Table I. We have also included for comparison in Table I the geometries obtained using the DIM semiempirical model, 3 since to our knowledge no high quality ab initio result is available for these systems. Nevertheless, we expect the DIM geometries to be quite accurate, as a good agreement with experiment was obtained by DIM calculations of evaporation energies for Xe n + → Xe n−1 + +Xe ͑Ref.…”

“…For linear Xe 3 + and linear Xe 4 + clusters we also optimized their geometries using DFT. We started our optimizations from previously published geometries 3 and used the Broyden-Fletcher-Goldfarb-Shanno conjugate gradient algorithm with a convergence criterion of 10 −3 eV/ Å in the forces on every atom. The calculation of the forces with the necessary accuracy required the use of a grid spacing of 0.3 Å.…”

“…This, of course, neglects all effects in the spectra due to the vibration of the nuclei. For each cluster size, we have calculated the absorption cross section for all the local mimina found in the DIM calculations by Pǎska et al 3 and then used this method to obtain a spectra at finite temperature. In Fig.…”

“…In our calculations, the position of the peak at around 3 eV is systematically redshifted with respect to the experimental value. The reason for the disappearance of this peak for n Ն 15 is due to the fact that few isomers have been found in the DIM calculations for those clusters, 3 as an extensive search in conformational space for such large clusters was prohibitive. The lack of experimental points for this peak makes it difficult to draw any further conclusions.…”

“…[4][5][6][7] Up to now, most theoretical studies of cationic xenon clusters made use of semiempirical methods, especially the "diatomics in molecules" ͑DIM͒ approach. The DIM method 8 has been quite successful in describing Xe clusters, both for the ground state 3,5 and their optical absorption. 6,7 In this approach, a model Hamiltonian is built using high quality ab initio diatomic data, such as energy surfaces of the neutral and the cationic dimer, both in the ground state and first excited state.…”