Tien Quang Nguyen

Nitric Oxide Adsorption Effects on Metal Phthalocyanines

The adsorption of nitric oxide (NO) on various metal phthalocyanines (MPc, M = Mn, Fe, Co) has been studied using first-principles calculations based on density functional theory (DFT). In this study, we investigated the fully optimized geometries and electronic structure of MPc. We found that the electronic structures of metal atoms are essential in shaping the ground-state electronic structure near the Fermi level. These states are defined mostly by the d orbitals of the transition-metal atoms and, to some degree, by the states of nitrogen and carbon atoms of the inner rings. The numerical calculations showed that NO strongly chemisorbs to the metal atom with an end-on configuration and results in a change in geometric and electronic structures of MPc. The N-O bond lengths are slightly longer than that of the isolated NO molecule. The orbital energy levels are shifted with respect to the Fermi level. The HOMO-LUMO gap widens as compared to bare MPc. These changes are attributed to the hybridization of the pi* orbital of NO and the d orbitals of the transition metal. Specifically, the interaction between dpi and the pi* orbital is significant for MnPc-NO, while the hybridization of d(z(2)) and the pi* orbital plays an important role in CoPc-NO.

The Adsorption of NO on Various Metal Tape-Porphyrins: A First-Principles Study

The adsorption of NO on various metal tape-porphyrins (Mn, Fe, and Co) is studied using first-principles calculations based on density functional theory (DFT). In this work we discuss the geometric structure and electronic properties of metal tape-porphyrins and the effect of the adsorption of NO on their properties. The results show that metal atoms protrude from the porphyrin plane toward the NO molecule. At the stable position, the variation of the metal–N–O angle is in the order: Co–N–O (123°) < Fe–N–O (148°) < Mn–N–O (180°). The N–O bond length in the metal tape-porphyrins is slightly longer than that of the isolated NO molecule. These results are consistent with other DFT calculations and experimental results. We also found that the binding energy of NO with metal porphyrins increases in the order CoTP–NO (1.718 eV) < FeTP–NO (1.719 eV) < MnTP–NO (1.736 eV). As regards the electronic properties, there is a metal–insulator transition in FeTP–NO. For CoTP–NO and MnTP–NO, we found that CoTP shows insul...

Molecular and Electronic Tuning of Si/Carbon Nanotube Hybrid System

In complex structures such as conjugated Si nanoparticles on carbon nanotubes (CNT), new properties arise out particle size control or nanoparticle–nanotube contact. In this work, the interaction of Si clusters (Sin, n=1–4) with metallic (5,5) single-wall carbon nanotube (SWCNT) is investigated using first principles calculations based on density functional theory, to show that electronic property of the Si/SWCNT system can change via Si–SWCNT conformation alone. Planar Si clusters on SWCNT exhibit the same metallic property regardless of size. However, once the planarity of Sin is lost, which happens when Si adsorption sites shifts towards the top and the Si–C bonds bend resulting to a buckled Sin configuration, a band gap of ~0.32 eV in the entire Si/SWCNT system is introduced. The migration behavior of Si adatoms shows ease of cluster formation due to surface curvature. Such cluster formation can be accommodated by a distortion in the C–C bonds of CNT. Mechanism for the opening of the SWCNT band gap is presented.