In order to construct our model Hamiltonian, we include symmetry unique pair interactions corresponding to three different symmetry unique intermolecular vectors, (i) the interactions with the nearest neighbour at the other 2c site in the cell, i.e. with an intermolecular vector of [ , -1 3 , 1 2 ] (and symmetry equivalent directions), (ii) the nearest neighbour along the c-directions at an intermolecular vector of [0, 0, 1] (and symmetry equivalent directions), and (iii) the next-nearest neighbour in the ab-plane with an intermolecular vector of [1, 0, 0] (and symmetry equivalent directions). This gives rise to 13, 6 and 12 symmetry unique interactions along the first, second and third intermolecular separations. All three types of interactions are needed in order to distinguish the experimentally observed ground state from specific defective states that we will consider below.