  The truncation of an optically thick, geometrically thin accretion disk is
investigated in the context of low luminosity AGN (LLAGN). We generalize the
disk evaporation model used in the interpretative framework of black hole X-ray
binaries by including the effect of a magnetic field in accretion disks
surrounding supermassive black holes. The critical transition mass accretion
rate for which the disk is truncated is found to be insensitive to magnetic
effects, but its inclusion leads to a smaller truncation radius in comparison
to a model without its consideration. That is, a thin viscous disk is truncated
for LLAGN at an Eddington ratio less than 0.03 for a standard viscosity
parameter ($\alpha = 0.3$). An increase of the viscosity parameter results in a
higher critical transition mass accretion rate and a correspondingly smaller
truncation distance, the latter accentuated by greater magnetic energy
densities in the disk. Based on these results, the truncation radii inferred
from spectral fits of LLAGN published in the literature are consistent with the
disk evaporation model. The infrared emission arising from the truncated
geometrically thin accretion disks may be responsible for the red bump seen in
such LLAGN.
