  The spin-1/2 XXZ chain in a uniform magnetic field at thermal equilibrium is
considered. For this model, we give a complete classification of all
qualitatively different phase diagrams for the one-way quantum work
(information) deficit. The diagrams can contain regions (phases, fractions)
with both stationary and variable (state-dependent) angles of optimal
measurement. We found cases of phase diagrams in which the sizes of regions
with the variable optimal measurement angle are large and perhaps such regions
can be detected experimentally. We also established a relationship between the
behavior of optimal measurement angles near the boundaries separated different
regions and Landau's theory of phase transitions of the second and first kind.
