  In certain configurations, the aromatic properties of benzene ring structured
molecules allow for unpaired, reactive valence electrons (known as radicals).
Clar's goblets are such molecules. With an even number of unpaired radicals,
these nanographenes are topologically frustrated hydrocarbons in which
pi-bonding network and topology of edges give rise to the magnetism. Clar's
goblets are therefore valued as prospective qubits provided they can be
modulated between magnetic states. Using first principles DFT, we demonstrate
the effects of adsorption on both molecule and substrate in a graphene-Clar's
goblet heterostructure. We look at the energy difference bewteen FM and AFM
states of the system and discuss underlying physical and chemical mechanisms in
reference to the highest occupied molecular orbital (HOMO) and second HOMO
(HOMO-1). We find that the HOMO of the molecule in the FM state is right at the
Fermi surface, which leads to the hybridization between molecular state and the
graphene state near the Dirac point. Furthermore, we investigate qualitative
changes in charge realignment and magnetic state under variable electric field.
Transitions from FM to AFM and back to FM states are observed.
