The aluminum phosphides AlmPn (m + n = 2-5) and their anions: structures, electron affinities and vibrational frequencies

Geometries, electronic states and electron affinities of AlnPm and AlnPm− (n + m = 2-5) clusters have been examined using four hybrid and pure density functional theory (DFT) methods. Structural optimization and frequency analyses are performed with the basis of 6-311 + G (2df) one-particle basis set. The geometries are fully optimized with each DFT method independently. Three types of energy separations reported in this work are the adiabatic electron affinity (EAad), the vertical electron affinity (EAvert), and the vertical detachment energy (VDE). The calculation results show that the singlet structures have higher symmetry than that of doublet structures. The best method for predicting molecular structures was found to be BLYP, while other methods generally underestimated bond lengths. The most reliable adiabatic electron affinities and vertical detachment energy, obtained at the 6-311 + G (2df)/BP86 level of theory, are 2.44 and 2.48 eV (Al2P), 2.03 and 2.24 eV (AlP2), 1.97 and 2.44 eV (AlP3), 2.01 and 2.10 eV (Al3P), 1.94 and 2.52 eV (Al2P2), 2.63 and 3.34 eV (AlP4), 2.10 and 2.48 eV (Al4P), 2.49 and 2.69 eV (Al2P3), 2.76 and 3.06 eV (Al3P2), respectively. Those for Al2P, AlP2, AlP3, Al3P, Al4P, and Al2P3 are in good agreement with experiment, but the predicted VDE values for Al2P2, Al3P2, and AlP4 are larger than the available experimental values. For the vibrational frequencies of the AlmPn 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 methods overestimate or underestimate the vibrational frequencies, with the worst predictions given by the BLYP method.