Many-Body Effects in FeN4 Center Embedded in Graphene

Abstract

We introduce a computational approach to study porphyrin-like transition metal complexes, bridging density functional theory and exact many-body techniques, such as the density matrix renormalization group (DMRG). We first derive a multi-orbital Anderson impurity Hamiltonian starting from first principles considerations that qualitatively reproduce generalized gradient approximation (GGA)+U results when ignoring inter-orbital Coulomb repulsion U ′ and Hund exchange J. An exact canonical transformation is used to reduce the dimensionality of the problem and make it amenable to DMRG calculations, including all many-body terms (both intra- and inter-orbital), which are treated in a numerically exact way. We apply this technique to FeN 4 centers in graphene and show that the inclusion of these terms has dramatic effects: as the iron orbitals become single occupied due to the Coulomb repulsion, the inter-orbital interaction further reduces the occupation, yielding a non-monotonic behavior of the magnetic moment as a function of the interactions, with maximum polarization only in a small window at intermediate values of the parameters. Furthermore, U ′ changes the relative position of the peaks in the density of states, particularly on the iron d z 2 orbital, which is expected to affect the binding of ligands greatly.

Single-Atom Catalysts as Promising Cathode Materials for Lithium–Sulfur Batteries

“…In this instance, we deployed GGA+ U calculations for capturing the strong interactions from the 3d– and 5d–electron transition metals. For the 3d–electron TMs, we obtained the Hubbard U value from the literature. − However, after thorough testing we identified that total energies, bond lengths, and the magnetic moment of the TM–N 4 –C (TM = Co, Fe, and V) structures with the appropriate U are similar to calculations with U = 0. Hence, we have concluded that a plain DFT approach is sufficient for our calculations.…”

Metal-N4@Graphene as Multifunctional Anchoring Materials for Na-S Batteries: First-Principles Study

“…M. Sajjad et al reported that polar nitrogenated holey graphene shows a superior anchoring of NaPSs [ 29 ]. Additionally, the co-doped graphene/carbon nanostructures are also reported to be intensively attractive, due to their novel geometries and properties [ 31 , 32 , 33 , 34 , 35 ]. For example, G. Xia et al reported that N and O co-doped porous carbon nanofibers could effectively alleviate the “shuttling effect” via adsorbing NaPSs by strong chemical interactions [ 31 ].…”

Electrochemical Potential of the Metal Organic Framework MIL-101(Fe) as Cathode Material in Li-Ion Batteries

“…Such an approach has been used in previous studies of MIL-101 materials [23][24][25][26][27] and other Fe-containing organometallics [20][21][22]. Beyond the van der Waals materials, cluster models have been successfully applied for the optimization of reduction activity of covalently bonded Fe-N4@graphene for fuel-cell fabrication [28][29][30]. In our work, this technique successfully unravels the mechanism of redox reactions in this MOF and opens a pathway for identifying irreversible Li intercalation reactions.…”