The arsenic clusters Asn (n = 1–5) and their anions: Structures, thermochemistry, and electron affinities

Abstract

The molecular structures, electron affinities, and dissociation energies of the As_n/As (n = 1–5) species have been examined using six density functional theory (DFT) methods. The basis set used in this work is of double-ζ plus polarization quality with additional diffuse s- and p-type functions, denoted DZP++. These methods have been carefully calibrated (Chem Rev 2002, 102, 231) for the prediction of electron affinities. The geometries are fully optimized with each DFT method independently. Three different types of the neutral-anion energy separations reported in this work are the adiabatic electron affinity (EA_ad), the vertical electron affinity (EA_vert), and the vertical detachment energy (VDE). The first dissociation energies D_e(As_n−1-As) for the neutral As_n species, as well as those D_e(As-As) and D_e (As_n−1-As⁻) for the anionic As species, have also been reported. The most reliable adiabatic electron affinities, obtained at the DZP++ BLYP level of theory, are 0.90 (As), 0.74 (As₂), 1.30 (As₃), 0.49 (As₄), and 3.03 eV (As₅), respectively. These EA_ad values for As, As₂, and As₄ are in good agreement with experiment (average absolute error 0.09 eV), but that for As₃ is a bit smaller than the experimental value (1.45 ± 0.03 eV). The first dissociation energies for the neutral arsenic clusters predicted by the B3LYP method are 3.93 eV (As₂), 2.04 eV (As₃), 3.88 eV (As₄), and 1.49 eV (As₅). Compared with the available experimental dissociation energies for the neutral clusters, the theoretical predictions are excellent. Two dissociation limits are possible for the arsenic cluster anions. The atomic arsenic results are 3.91 eV (As → As⁻ + As), 2.46 eV (As → As + As), 3.14 eV (As → As + As), and 4.01 eV (As → As + As). For dissociation to neutral arsenic clusters, the predicted dissociation energies are 2.43 eV (As → As₂ + As⁻), 3.53 eV (As → As₃ + As⁻), and 3.67 eV (As → As₄ + As⁻). For the vibrational frequencies of the As_n series, the BP86 and B3LYP methods produce good results compared with the limited experiments, so the other predictions with these methods should be reliable. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 907–920, 2004