A study on the stability of O2 on oxometalloporphyrins by the first principles calculations

Silicon is of special interest in lithium-ion batteries (LIBs) since it has large theoretical specific capacity or volumetric capacity. The crystal structure, charge distribution and density of states of LiSi as the Li-poorest side compound at the start of Li intercalation mechanism for Si anode in LIBs has been studied by using Density Functional Theory calculations. The triangular pyramids are formed by four Li atoms. Compared with the charge density of crystalline Si, the Si-Si covalent bonds in LiSi become weak due to Li intercalation. On the other hand, the electrons around the Li atoms in LiSi increase compared with metallic Li. The Li atoms in LiSi have negative charge of 0.830～0.843 compared with metallic Li. These electrons, which are transferred from p electrons in the Si atoms, are mainly made of p electrons of the Li atoms. When considering the lithium intercalation reaction from crystalline Si to LiSi, the average intercalation voltage is 0.4053 V

Mounting a hydrogenase analog on calixarenes—designing a nature-inspired solid state catalyst for fuel cells by density functional theory

The hydrogen-fuel PEFC (polymer electrolyte fuel cell) is among the most promising alternative power generators of the future. But for it to become widely used, an alternative catalyst to platinum must be developed. While there have been previous attempts to synthesize hydrogenase mimics for this purpose, the current state of artificial hydrogenases can be summarized into two groups: sufficiently active but not in a stable solid state; and in the solid state but not sufficiently active. We model a modified active site of Fe-only hydrogenases deposited on a variety of calixarenes for solid-state support by density functional calculations. Among the calixarenes considered, our calculations have shown that calix[5]arene is so far the most viable macrocycle to hold the di-iron site. Our calculations also show that the crucial hydrogenase active site characteristics are maintained in this material: having an Fe--Fe bond and anti-bond at the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) respectively; and the bonding orbitals on the Fe centers connected to the sulfur of the electron chain at the HOMO

A density functional analysis on the photoelectronic spectra of Fe-only hydrogenase analogues

Density functional theory calculations have been performed on Fe-only hydrogenase analogues compounds [(i-PDT)Fe2(CP)4(CN) 2]2- (compound I) and [Fe2(CC) 4MeSCH2C(Me)-(CH2S)2(CN)]- (compound II). Results using BPW91/6-311+G(d,p) show electron affinity and trends in molecular orbitais consistent with photoelectron spectroscopy data. The HOMO orbitais show familiar Fe-Fe bonding characteristics while the LUMO orbitais show Fe-Fe anti-bonding characteristics. To compare the effects of a second CN versus a terminal sulfur ligand, results for compound I after one electron is removed (compound 1-1e) were compared with those of compound II. It was found that compound I-1e has a much lower HOMO. Mulliken charge analysis also shows that the terminal sulfur has a stronger electron donating effect than a CN ligand. From the standpoint of computational materials design, we therefore think that similarities in electron affinity, 2Fe charge density and HOMO/LUMO characteristics to the biologically present active site should be bases for predicting catalytic activity of Fe-only hydrogenase analogues. © 2007 The Surface Science Society of Japan

First principles study of electric and magnetic properties of benzene-iron multiple-decked sandwich chain

We investigate electric and magnetic properties of a benzene-iron multiple-decked sandwich chain [Fe(C6H6)] ∞. By performing first principles calculation based on the density functional theory, we find that the system [Fe(C6H 6)]∞ is stable and has no magnetic moment for which the two succeeding iron atoms are antiferromagnetically arranged. We propose a superexchange interaction mechanism for this antiferromagnetic order. ©2006 The Physical Society of Japan

A first principles investigation on the interaction of oxomolybdenum porphyrin with Q2 - Oxomolybdenum porphyrin as a catalyst for oxygen reduction

We investigated the interaction of oxomolybdenum porpyhrin (MoO(por)) with 0% by using first principles calculations. Our calculations indicate that the adsorbed O2 on MoO(por) does not take an end-on configuration, but a side-on configuration to become more stable. These results can be understood from the differences in the molecular orbital energies and the valence electron densities. The geometric parameters of MoO(por) and MoO(por) (O2) with a side-on configuration of O2 are in good, agreement with experimental results. © 2006 The Surface Science Society of Japan