creates magnetic Hamiltonian with a single command
QUICKHAM(obj, J)
The function generates the bonds from the predefined crystal structure
and assigns exchange values to bonds such as J(1) to first neighbor, J(2)
for second neighbor etc. The command will erase all previous bond,
anisotropy, g-tensor and matrix definitions. Even if J(idx) == 0, the
corresponding bond and matrix will be created.
Input:
obj Spinw object.
J Vector containing the Heisenberg exchange values. J(1) for
first neighbor bonds, etc.