Comparison of experimental and theoretical structure amplitudes and valence charge densities of GaAs

The current best sets of X-ray structure amplitudes for GaAs, gallium arsenide, are completed by highly precise data recorded at 0.50 < sin theta/lambda < 1.35 Angstrom(-1). For the strong reflections the required accuracy of Delta F/F less than or equal to 1% was realized by the use of Pendellosung measurements at lambda = 0.30 Angstrom, recording the integral intensities as a function of the effective thickness from similar to 500 mu m thick GaAs wafers. Additionally, several weak reflections were determined from their integral intensities within the kinematic limit at wavelengths lambda = 0.3, 0.56 and 0.71 Angstrom. From these data individual Debye-Waller factors for gallium and arsenic were determined using the model of independent spherical atoms [B-Ga = 0.666 (4) and B-As = 0.566 (4) Angstrom(2)]. The extended set of experimental structure factors now available is compared with those obtained by ab initio solid-state Hartree-Fock (HF) and density functional (DF) calculations. Therefore, the theoretical data were adapted to room temperature using the experimentally evaluated Debye-Waller factors and the model mentioned above. The valence and difference charge densities obtained from experimental and theoretical data show the expected charge accumulation between nearest neighbours slightly shifted towards the arsenic site. The disagreement remaining between the experimental and theoretical data, on the one hand, and between those of both ab initio methods, on the other hand, are of the same order of magnitude.