Eur. Phys. J. D 42, 259-267 (2007)
https://doi.org/10.1140/epjd/e2007-00041-9

The aluminum arsenides Al_mAs_n (m + n = 2–5) and their anions: Structures, electron affinities and vibrational frequencies

School of Chemistry and Material Chemistry, Shanxi Normal University, Linfen, 041004, P.R. China

Corresponding author: ^a gl-guoling@163.com

Received: 27 June 2006
Revised: 14 September 2006
Published online: 28 February 2007

Abstract

Geometries, electronic states and electron affinities of Al_mAs_n and Al_mAs_n (m+n=2–5) clusters have been examined using four hybrid and pure density functional theory (DFT) methods. Structural optimization and frequency analyses are performed using a 6-311+G(2df) one-particle basis set. The geometries are fully optimized with each DFT method independently. The three types of 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 calculation results show that the singlet structures have higher symmetry than that of doublet structures. The best functional for predicting molecular structures was found to be BLYP, while other functionals generally underestimated bond lengths. The largest adiabatic electron affinity, vertical electron affinity and vertical detachment energy, obtained at the 6-311+G(2df)/BP86 level of theory, are 2.20, 2.04 and 2.27 eV (AlAs), 2.13, 1.94 and 2.38 eV (AlAs₂), 2.44, 2.39 and 2.47 eV (Al₂As), 2.09, 1.80 and 2.53 eV (Al₂As₂), 2.01, 1.57 and 2.36 eV (AlAs₃), 2.32, 2.11 and 2.55 eV (Al₂As₃), 2.40, 1.45 and 3.26 eV (AlAs₄), 1.94, 1.90 and 2.07 eV (Al₄As), respectively. However, the BHLYP method gives the largest values for EA_ad and EA_vert of Al₃As and EA_ad of Al₃As₂, respectively. For the vibrational frequencies of the Al_nAs_m series, the B3LYP method produces good predictions with the average error only about 10 cm^-1 from available experimental and theoretical values. The other three functionals overestimate or underestimate the vibrational frequencies, with the worst predictions given by the BHLYP method.