Mohammad Kemal Agusta

Theoretical Study on Hydrazine Chemisorption on Transition Metal Surfaces

Theoretical study on hydrazine adsorption on transition metal surfaces is conducted using the density functional theory. The study is focused on the trend of stability of hydrazine on several trans...

First principles calculation on the adsorption of water on lithium?montmorillonite (Li?MMT)

The interaction of water molecules and lithium-montmorillonite (Li-MMT) is theoretically investigated using density functional theory (DFT) based first principles calculation. The mechanism of water adsorption at two different water concentrations on Li-MMT as well as their structural and electronic properties are investigated. It is found that the adsorption stability in Li-MMT is higher in higher water concentration. It is also found that an adsorbed water molecule on Li-MMT causes the Li to protrude from the MMT surface, so it is expected that Li may be mobile on H(2)O/Li-MMT.

Density functional study of adsorptions of CO2, NO2 and SO2 molecules on Zn(0002) surfaces

We report on a theoretical study of adsorptions of CO2, NO2 and SO2 molecules on ZnO(0002) surfaces using density functional theory-based (DFT-based) calculations. These adsorptions are done on perfect and defective ZnO(0002) surfaces. We find that all of these molecules are chemically adsorbed on the perfect ZnO(0002) surface. In the presence of Zn vacancy, we find that the surface is only active toward SO2 molecule. On the hydroxylated ZnO(0002) surfaces, CO2 and SO2 molecules can react with the preadsorbed OH molecule to form various adsorbates such as: carboxyl (COOH), bicarbonate (CO3H), sulfonyl hydroxide (SO3H), SO3 and water. However, NO2 molecule cannot react with the pre-adsorbed OH molecule and only physically adsorbed on the surface.

DFT study of adsorption of CO2 on palladium cluster doped by transition metal

We report on a theoretical study of CO2 adsorption on Pd6-M (M: Ni, Cu, Pt, Rh) cluster using first-principles density functional theory (DFT) calculations. We find that CO2 molecule is adsorbed with a bidendate configuration on Pd7 and on most of Pd6M clusters. The bidendate adsorption configuration is formed due to the filling of the unoccupied n* orbital of CO2 molecule upon its interaction with d-orbitals of the cluster. We find that transition metal doping could modify the adsorption energy, adsorption site and adsorption configuration of CO2 molecule on Pd7 cluster. We also predict that the usage of Pd6M clusters as CO2 hydrogenation catalysts might facilitate the formations of HCOO/COOH.

Dipole Strength Calculation Based on Two-Level System Approximation to Study Q/B-Band Intensity Ratio of ZnTBP in Solvent

We study the Q/B-band dipole strength of zinc tetrabenzoporphyrin (ZnTBP) using density functional theory (DFT) in various solvents. The solvents are modeled using the polarized continuum model (PC...

Cr, Fe - Doped Anatase TiO2 Photocatalyst: DFT+U Investigation on Band Gap

Photocatalytic hydrogen generation holds promise as the future source of environmentally friendly and economically feasible energy source. In order to conduct more efficient photocatalytic reaction, anatase TiO2 doped with transition metals is proposed as catalyst. Investigation was conducted by using density functional theory (DFT) augmented with Hubbard U treatment to correct the band gap of TiO2. Emergence of new states inside the band gap of doped anatase TiO2 can lead to a material with a better photocatalytic property, i.e., able to work at visible light than that of pristine TiO2 which is sensitive to UV light only. The investigated materials comply with standard hydrogen electrode (SHE), thus can be used as photocatalyst in water splitting reaction. Out of the two options tested, TiO2 doped with Fe produces a material with the better photocatalytic properties.Keywords: DFT + U, anatase TiO2, photocatalytic, water splitting, band gap

Frontier Orbitals of Dehydrogenated Tetrahydrocurcumin in Water Solvent: A Theoretical Study

We studied two frontier orbitals - the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO)- of tetrahydrocurumin (THC) using density-functional theory (DFT) in water solvent. These orbitals were observed in THC molecule without one hydrogen atom (dehydrogenated THC). The loss of hydrogen atom is due to the transfer of the atom from THC molecule toward reactive oxygen species (ROS) (Hydrogen atom transfer –HAT- mechanism). We began our investigation by optimizing dehydrogenated THC at three X-H sites. Then, water solvent was added by using polarized continuum model (PCM) method. This study observed that dehydrogenated THC at two O-H sites has wider gap of HOMO-LUMO compare to C-H site.

Enhanced molecular adsorption of ethylene on reduced anatase TiO2 (001): role of surface O-vacancies

A density functional theory (DFT)-based study of ethylene (C2H4) adsorption on a reduced anatase titanium dioxide (TiO2) (001) surface, i.e., with a surface oxygen vacancy (Ovac), is presented. It was found that C2H4 preferably adsorbs on the Ovac-site. The excess electrons originating from the removed oxygen weaken the C2H4 CC double bond by filling the lowest unoccupied molecular orbital (LUMO) or of C2H4, and simultaneously enhance the binding of C2H4 to the reduced anatase TiO2 (001). The bonding between the two C2H4 C atoms and the two Ti atoms nearest to the Ovac-site produces two σ-type bonds, leading to the emergence of a new localized mid-gap state. This hybrid 3d defect state can account for the ∼0.7 eV decrease in the band-gap observed in previous optical measurements of carbon-coated TiO2, formed after TiO2 exposure to C2H4 gas (Mater. Lett. 108, 2013, 134). Subsequent calculations on two initial decomposition pathways of C2H4 adsorbed on the Ovac-site show that the C–H bond and C–C bond cleaving require high activation barriers where the C–H bond cleaving is slightly easier compared to the C–C bond cleaving, 2.94 eV and 3.01 eV, respectively, (as calculated using DFT-D2+Ud = 3 eV) and the final states of the two initial decomposition pathways show similar endothermic characteristics. This finding indicates that the surface Ovac-sites tend to favor the formation of molecularly adsorbed Ti-bound sp3-C2H4 (–Ti–CH2CH2–Ti–) as compared to the dissociative adsorption case.

DFT study of the formate formation on Ni(111) surface doped by transition metals [Ni(111)-M; M=Cu, Pd, Pt, Rh]

We report on a theoretical study of the formation of formate (HCOO) from the reaction of CO2 gas and a pre- adsorbed H atom (CO2 (g) + *H → *HCOO) on Ni(111) surface doped by transition-metals [Ni(111)-M; M= Cu, Pd, Pt, Rh] by means of density functional theory (DFT) calculations. This *HCOO formation reaction is one of the most important rate- limiting steps in the methanol synthesis process. We find that the presence of transition metal doping on the first-layer of Ni(111) surface could reduce the activation barrier of this reaction [up to ~38.4%, compared to clean Ni(111) surface].

First-Principles Molecular Dynamics Study on Helium- filled Carbon Nanotube

Investigation on carbon nanotube (CNT) filled by Helium (He) atoms is conducted using Density Functional Theory and Molecular Dynamics Simulation. It reveals that He atom is repelled by CNTs wall and find its stable position at the tube center. Vibrational analysis on modes corespond to radial inward and outward breathing movement of CNT shows that He filling tends to pull the CNT wall in inward direction. Furthermore, examination on C-C stretch mode reveals that the existence of He improve the stiffness of CNTs wall. Molecular dynamics calculations which are done on (3,3) and (5,5) nanotube with 0.25 gr/cm3 and 0.5 gr/cm3 He density at 300 K and 1500 K confirms the increase of stiffness of CNT wall by interaction with He atoms. Effects of variation of chirality, temperature and He density on CNT wall stiffness is also reported.