Hyperpolarizability of GaAs dimer is not negative

We present a systematic study of the static electric hyperpolarizability of Ga2As2. The authors rely on finite-field high-level ab initio calculations with carefully optimized basis sets. Their best values for the mean and the anisotropy of the dipole polarizability are (alpha) over bar = 158.57 and Delta alpha = 130.33e(2)a(0)(2)E(h)(-1). For the hyperpolarizability we propose an estimate (gamma) over bar = (155 +/- 15) x 10(3)e(4)a(0)(4)E(h)(-3), which does not agree with the negative value predicted by Lan et al. [J. Chem. Phys. 124, 094302 (2006)]. Density functional theory based methods yield values close to those predicted by conventional ab initio methods. The (hyper) polarizability components are particularly enhanced along the direction defined by the Ga - Ga axis. (c) 2007 American Institute of Physics.