  We present a Monte Carlo study of external surface anchoring in nematic cells
with partially disordered solid substrates, as well as of intrinsic anchoring
at free nematic interfaces. The simulations are based on the simple hexagonal
lattice model with a spatially anisotropic intermolecular potential. We
estimate the corresponding extrapolation length $b$ by imposing an elastic
deformation in a hybrid cell-like nematic sample. Our estimates for $b$
increase with increasing surface disorder and are essentially
temperature--independent. Experimental values of $b$ are approached only when
both the coupling of nematic molecules with the substrate and the anisotropy of
nematic--nematic interactions are weak.
