Eben Sy Dy

Comparative study of O2 dissociation on various metalloporphyrins.

We investigate O(2) interaction with various metalloporphyrins (MnP, FeP, CoP, and NiP) using ab initio calculations based on density-functional theory. We discuss the trends in the activation barriers for the O-O bond cleavage in relation to the geometric, vibrational, electronic, and energetic properties of the systems. Whether the lowest unoccupied molecular orbital-highest occupied molecular orbital (LUMO-HOMO) levels of the metalloporphyrins involve the corresponding metal centers depends on the d orbital occupancies of the metals. We found that activation barriers for the O(2) dissociation can be mainly determined from the LUMO-HOMO characters of the metalloporphyrins, and consequently the FeP is the best catalyst with respect to the O(2) interaction from adsorption to dissociation.

Theoretical Investigation of Electric and Magnetic Properties of Benzene–Vanadium Sandwich Complex Chain

We investigate the electric and magnetic properties of a benzene–vanadium complex chain [V(C6H6)]∞. By performing first principles calculation based on the spin-polarized density functional theory, we find that this system shows a half metallic ferromagnetic behavior, i.e., majority-spin (spin-up) electrons have a semiconducting band gap, while minority-spin (spin-down) electrons are metallic. We suggest that this ferromagnetic order is due to a double-exchange mechanism.

Adsorption of O2 on Cobalt-(n)Pyrrole Molecules from First-Principles Calculations

In order to clarify the adsorption mechanism of the O 2 molecule on Co–polypyrrole composite metallo-organic catalyst, we have investigated the interaction between the molecule and Co–( n )pyrrole model clusters ( n =4,6) using the density functional theory. The stable adsorption site of the O 2 molecule on Co–(4)pyrrole is found to be at the O–O center of mass located on top of the Co atom in side-on configuration, while for the case of Co–(6)pyrrole cluster, the O 2 molecule is slightly deviated from the side-on configuration. The O–O bonds of the O 2 /Co–(4)pyrrole and the O 2 /Co–(6)pyrrole systems have elongated by 10.84 and 9.86%, respectively. The elongation mechanism of O 2 on Co–( n )pyrrole is induced by the interaction between the cobalt d -orbitals and the O 2 anti-bonding π * orbital, which results in a charge transfer from the cobalt atom toward the O 2 molecule. This effect seems important in the adsorption of the O 2 molecule on Co–( n )pyrrole. It is likely that the extra charge in the O ...

CO adsorption effects on the electronic properties of Fe tape-porphyrin

We investigated the electronic properties of Fe tape-porphyrin and the effect of CO adsorption on it within the framework of density functional theory. As for the numerical results, we found that the Fe tape-porphyrin is metallic, and that the CO-adsorbed Fe tape-porphyrin is an insulator. Comparing the electronic structures of the Fe porphyrin molecule and the CO-adsorbed one, we found that the metal-insulator transition is caused by the hybridization of the d(xz) and d(yz) orbitals of Fe with the π(g)(*) orbital of CO.

Exploring haem-based alternatives for oxygen reduction catalysis in fuel cells—a status report of our first principles calculations

For hydrogen fuel cells to become commercially viable, an alternative catalyst to platinum surfaces that is both efficient and affordable must be discovered. We consider haem and haem derivatives as potentials substitutes. In this paper, we discuss the oxygen reduction reaction on both the platinum surface and on haem. We then introduce our suggestions based on density-functional studies on how to improve haems oxygen-reduction capabilities, which can be summarized as follows: inducing the singlet state, inducing side-on interaction, mimicking cytochrome c oxidase by adding a copper-imidazole complex, using platinum deposited on tin porphyrin instead of haem, and using oxomolybdenum porphyrin instead of haem. We shall focus on the last three methods because of their experimental practicability.

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

The authors investigated the interaction of oxometalloporphyrins (MO(por))--specifically, MoO(por), WO(por), TiO(por), VO(por), and CrO(por)--with O(2) by using first principles calculations. MoO(por) and WO(por) undergo reactions with O(2); on the other hand, TiO(por), VO(por), and CrO(por) do not. Next, they compared the interaction of MoO(por) and WO(por) with O(2). Activation barriers for the reactions of MoO(por) and WO(por) with a side-on O(2) are small. For MoO(por)(O(2)), the activation barrier for the reverse reaction that liberates O(2) is also small; however, that for WO(por)(O(2)) is large. The experimental results that photoirradiation with visible light or heating of Mo (VI)O(tmp)(O(2)) regenerates Mo (VI)O(tmp) by liberating O(2) while W (VI)O(tmp)(O(2)) does not [J. Tachibana, T. Imamura, and Y. Sasaki, Bull. Chem. Soc. Jpn. 71, 363 (1998)] are explained by the difference in activation barriers of the reverse reactions. This means that bonds formed between the W atom and O(2) are stronger than those between the Mo atom and O(2). The bond strengths can be explained by differences in the energy levels between the highest occupied molecular orbital of MoO(por) and WO(por), which are mainly formed from the a orbitals of the central metal atom and pi(*) orbitals of O(2).

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(C 6 H 6 )] ∞ . By performing first principles calculation based on the density functional theory, we find that the system [Fe(C 6 H 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.