electric-field-induced triplet to singlet transition in size-2 trigonal zigzag graphene nanoflake

using hartree-fock su-sheriffer-heeger (hf-ssh) model, we have studied the dependence of the energies of the ground (magnetic triplet state) and the first exited (nonmagnetic singlet state) states of the size-2 trigonal zigzag graphene nanoflake (size-2 nf) on the intensity of an external in plane static electric field at zero temperature. we identify a transition from the magnetic triplet state to a nonmagnetic singlet state in size-2 nf caused by the polarization energy induced by the in plane static electric field. this transition has a unique property of being accompanied by a sudden increase in the electric dipole moment of the size-2 nf.