J5 interactions 
% according to the chirality (J5>J3).
% * epsilon_Delta: Chirality of the triangular units.
% * epsilon_H: Sense of rotation of the spin helices along the c-axis
% (right handed rotation is positive).
% The three property are related:
% eT = eD*eH.

eD = -1;
eH = +1;
eT = eD*eH;

%% Magnetic Hamiltonian
% We define the magnetic Hamiltonian depending on the epsilon_T crystal
% chirality. We neglect the Dzyaloshinskii-Moriya interaction, that can be
% introduced in a straightforward manner.

