A multislice formalism of Cowley and Moodie [Acta Crystallogr. 10 (195
7) 609] with a recently developed edge-patching method has been applie
d to quantitative analyses of RHEED patterns from MBE grown GaAs(001)-
2 x 4 surfaces. The analyses are based on the ordering of visually est
imated spot intensities of several observed RHEED patterns from the Ga
As(001)-2 x 4 surfaces. The surface structure is proved to be a dimeri
zed vacant 2 x 4 reconstruction missing one dimer of every four along
the [110] direction, which is consistent with previous STM observation
s. The relaxation of the top layer is found to be about delta = + 8.0%
(0.113 angstrom). The results give an overall Debye-Waller factor of
B = 0.35 angstrom2 and a crystal absorption of alpha = 0.1 for the con
ditions at which the observed RHEED patterns were acquired. The effect
s of dimer twist on the intensities of RHEED patterns are briefly asse
ssed. This indicates that twist of dimers on the GaAs(001)-2 x 4 surfa
ce is unlikely. Errors involved in the calculations are also discussed
.