  We demonstrate numerically that for the strongly anisotropic homometallic S=2
canted single-chain magnet described by the quantum antiferromagnetic
Heisenberg model the correlation energy and exchange coupling constant can be
directly estimated from the in-field-magnetization profile found along the
properly selected crystallographic direction. In the parameter space defined by
the spherical angles (\phi, \theta) determining the axes orientation, four
regions are identified with different sequences of the characteristic
field-dependent magnetization profiles representing the antiferromagnetic,
metamagnetic and weak ferromagnetic type behavior. These sequences provide a
criterion for the applicability of the anisotropic quantum Heisenberg model to
a given experimental system. Our analysis shows that the correlation energy
decreases linearly with field and vanishes for a given value H_{cr} which
defines a special coordinates in the metamagnetic profile relevant for the
zero-field correlation energy and magnetic coupling. For the single-chain
magnet formed by the strongly anisotropic manganese(III) acetate
meso-tetraphenylporphyrin complexes coupled to the phenylphosphinate ligands,
the experimental metamagnetic-type magnetization curve in the c direction
yields an accurate estimate of the values of correlation energy
\Delta_{\xi}/k_B = 7.93 K and exchange coupling J/k_B=1.20 K.
