Multiplets in a ligand-field are treated within total-energy density functional calculations by imposing density matrix constraints on the d-orbital occupation numbers consistent with the local site and state symmetries. We demonstrate the utility of this approach for the case of isolated Fe phthalocyanine (FePc) molecules with overall D 4h symmetry: We find three stationary states of 3 Eg, 3 A2g, and 3 B2g symmetries of the Fe 2+ ion and total energy calculations clearly demonstrate that the ground state is 3 A2g. By contrast, a columnar stacking of the FePc molecules (α-FePc) is found to change the ground state to 3 Eg due to hybridization between adjacent molecules.
The realization of single molecular electronics is considered the next frontier to addressing and sustaining the storage needs of the future. In order to realize a single molecular device working at 300 K, two conditions must be satisfied: firstly, there must be no molecular diffusion, i.e., robust bonding between molecules and the contacting electrode, and secondly, stable electronic interface states. In this study, using a combination of 7-K and 300-K ultrahigh vacuum scanning tunneling microscopy/spectroscopy experiments and theoretical ab-initio calculations, we investigated the adsorption of π-conjugated metal-free phthalocyanine (Pc) single molecules onto an Fe(001) whisker single crystal along with the resulting electronic interface structures. The Pc/Fe(001) system was found to prevent molecular diffusion even at 300 K, due to strong adsorption as well as the presence of a larger diffusion barrier than that of the Pc/Ag(001) system, in which molecules are known to diffuse at 300 K. The origin of such a robust bonding was studied by recovering the sample local density of states (LDOS) with the normalized (dI/dV)/T curves, which LDOS peaks are successfully explained by theoretical calculations.
Electronic configurations and magnetic anisotropy of organometallic metallocenes (MCp2s) were investigated by means of first principles calculations based on the constraint density functional theory. The results predict that the ground states for M = Cr, Mn, Fe, Co, and Ni are the E32g,E22g,A11g,E21g, and A32g states, respectively. The magnetizations of the CoCp2 and NiCp2 energetically favor highly orienting along the perpendicular and parallel directions to the cyclopentadienyl (Cp) plane, respectively, and the others show almost no preference for the magnetic easy axis.
Magnetism and multiplets for metal-phthalocyanine (MPc) molecules with transition-metals (M) of Mn and Co were investigated based on the constraint density functional theory calculations by imposing density matrix constraint on the d-orbital occupation numbers. For the MnPc, the ground state is found to be the 4 E g state with the perpendicular magnetic anisotropy with respect to the molecular plane, while for the CoPc, the ground state is the 2 A 1g state with a planar magnetic anisotropy. V C 2013 American Institute of Physics. [http://dx
The ground state electronic configurations of the correlated organometallic metallocenes, MCp2, M = V, Cr, Mn, Fe, Co, and Ni, are investigated using constraint density functional theory combined with non-empirical U eff parameters determined from linear response theory. The relative stability of the various d-orbital electronic configurations of these organometallic molecules is found to be sensitive to the amount of correlation. Using non-empirical values of U eff , the calculated electronic configurations are in agreement with the experiments:
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