Density-Functional Calculations on the Spin Dependence of Aminoferrocene on Graphene*

In recent work, El-Gendy et al., strong magnetism in aminoferrocene–graphene molecular magnets [Appl. Phys. Lett. 5 June 2023] was reported. They identified a complex formed from ferrocene and graphene that exhibits anomolously large magnetic behavior. Motivated by that observation, they followed up with a paper analyzing the possibility of a chiral arrangement of six amino ferrocenes [Appl. Phys. Lett. 124, 111903 (2024)]. The electronic and vibrational spectra of aminoferrocene as a function of charge and spin in Aminoferrocene is interesting because the energy of the neutral molecule exhibits very small Hunds-rule preference for high spin and vibrational zero-point energies can impact the energy splitting. Further, the charged systems exhibit reasonably strong magnetic anisotropy which itself is dependent on the degree of ionicity and spin of the system. When the chiral complex is placed above a substrate, such as graphene, the charge may depend on the relative electronegativities of the substrate and the ring. Further the magnetic strength of the system depends on the charge state. We used the density functional theory (DFT) to study the electronic and vibration spectra of aminoferrocene. First, we relaxed the structure of aminoferrocene to find the most stable geometry. We computationally determined how the properties of molecule change for two different spin states (S=1 & S=2) and we looked at what happens by either addition or reduction of one electron from both spin states (by making them anion & cation). Vibrational calculations vs spin and charge state can determine if vibrational spectra can identify total moments and total charges. For all vibrational calculations, we have some imaginary frequencies which require anharmonic calculations. Our main goal is to find out about the charge transfer from aminoferrocene to graphene or graphene to aminoferrocene. We will report on electronic and vibrational spectra that may be used to determine the spin and charge states of the molecule and compare results of monomers on graphene to hexamers on graphene and periodic arrays of hexamers on graphene.