Triati Dewi Kencana Wungu

A first-principles study on defect association and oxygen ion migration of Sm3+ and Gd3+ co-doped ceria

First-principles calculations based on density functional theory were performed to investigate the co-doping effects of Sm and Gd in ceria on its oxygen ion conduction. The focus of this study is on the interactions between the cation dopants and an oxygen vacancy within the two adjacent tetrahedral sites of fluorite structure surrounding the oxygen migration path. Vacancy formation energies, dopant-vacancy association energies, and migration energies were calculated to elucidate the doping effects on oxygen ion conduction. The migration energies show remarkable dependences on the ionic radii of the cations located at the edges of the migration path. A simple relation between migration energy and vacancy formation energy is proposed. This work provides an informative insight into vacancy diffusion that could be useful in optimizing doping materials for improving oxygen ion conductivity in doped ceria.

Analysis of structural and electronic properties of Pr2NiO4 through first-principles calculations

The structural and electronic properties of bulk Pr(2)NiO(4+δ) (δ = 0 and 0.031) were analyzed using first-principles calculations based on the density functional theory (DFT) for application to electrode materials in solid-oxide fuel cells (SOFCs). Two structures of Pr(2)NiO(4) were analyzed: one in space group I4/mmm associated with the high temperature tetragonal (HTT) structure, and the other in Bmab with the low temperature orthorhombic (LTO) structure. The main difference between the two structures is the pronounced tilting of the nickelate octahedra found in the Bmab structure. Here, we will show that the difference in the electronic properties between the two structures, i.e. half-metallic for the I4/mmm structure and metallic for the Bmab structure, is attributed to the tilting of the nickelate octahedra. Furthermore, we found that the presence of interstitial O atoms at the Pr(2)O(2) bilayers is responsible for the tilting of the octahedra and thus is a dominant factor in the transition from the I4/mmm structure to the Bmab structure. These results would be of great significance to materials design related to the enhancement of O diffusivity in this material.

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.

The study of electronic structure and properties of silicene for gas sensor application

In this study, we investigated the adsorption of gas molecules (H2S, CO) on pristine silicene using first principles calculation. The structure, electronic properties, and adsorption energy of H2S,CO/silicene are discussed thoroughly. We found that the pristine silicenewith low buckling structure is the most stable as compared with planar and high buckling structures. Silicene was able to detect a gas molecule which can be observed according tothe density of states analysis. Though a gas molecule adsorbed weakly, the electronic properties of the low buckling pristine silicene changed from semi-metal (zero band gap) to semiconductor. The adsorption energy of H2S and CO on silicene is 0.075 eV and 0.06 eV, respectively.

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.

Effect of Lithium Absorption at Tetrahedral Site and Isomorphic Substitution on Montmorillonite Properties: A Density Functional Theory Study

This study deals with the effect of the isomorphic substitution on the sorption of two Li atoms on montmorillonite using density functional theory (DFT). The isomorphic substitution is carried out by modifying the atomic composition of the upper tetrahedral layer of the montmorillonite by replacing one Si atom with one Al atom on the said position. Note that in the conventional structure, Si atom is located at the upper tetrahedral layer of montmorillonite. Results show that one Li atom is likely to be situated in the vacant tetrahedral site and the other one is in the vacant octahedral site, for both of the two montmorillonite systems (isomorphic substitution and conventional structure). The sorption energy was found to be -6.31 eV at the most stable configuration, that is for the isomorphic substitution.

Study on transport properties of silicene monolayer under external field using NEGF method

We investigate the current-voltage (I-V) characteristics of a pristine monolayer silicene using non-equilibrium Green function (NEGF) method combining with density functional theory (DFT). This method succeeded in showing the relationship of I and V on silicene corresponding to the electronic characteristics such as density of states. The external field perpendicular to the silicene monolayer affects in increasing of the current. Under 0.2 eV external field, the current reaches the maximum peak at Vb = 0.3 eV with the increase is about 60% from what it is in zero external field.

Stability and electronic properties of defective single walled carbon nanotubes (CNTs)

In this project we using density functional theory (DFT) to investigate stability and the changes of electronic properties of single walled carbon nanotubes (SWCNT) defect by vacancy. We chosen a (10,0) and (8,0) SWCNT pristine geometry which have zigzag structure. We observed that defect not only can affect the changes of properties such as energy, bond length, and deformation of CNT structures, but also the stability and the electronic properties of CNT. The changes of various bond length of atoms around the vacancies area about 0.051 A0smaller or 0.1 A0 larger than the original C-C bond length. In addition, by calculating the formation energy, it gives us information that divacancy or V2 is the most stable vacancy. Numbers of vacancy make an electronic properties transition from semiconductor to metal.

Ab-Initio Calculation of Electronic Structure of Lead Halide Perovskites with Formamidinium Cation as an Active Material for Perovskite Solar Cells

Organic lead halide perovskite material based solar cells show impressive power conversion efficiencies, which can reach above 19 percent for perovskite solar cell with methyl-ammonium cations. These efficiencies are originated from efficient photoexcitation and charge carrier transport and not observed in conventional perovskite crystals. In this preliminary research work, we therefore performed Density Functional Theory (DFT) calculation of formamidinium lead iodide (FAPI), an alternative to methyl-ammonium lead iodide (MAPI), to predict their electronic structure and density of state (DOS). The calculation result at the most stable lattice parameters show a good agreement with the experiment results. The obtained band gap energy is 1.307 eV. The valence band is dominantly formed by the 5p orbitals of I- anions, while the conduction band is dominantly formed by the 6p orbitals of Pb2+ cations. The DOS of valence band of this perovskite seems smaller compared to the case of methyl-ammonium lead iodide perovskite, which then may explain the observation of smaller power conversion efficiencies in perovskite solar cells with this formamidinium cations.

Density Functional Theory (DFT) Study of Molecularly Imprinted Polymer (MIP) Methacrylic Acid (MAA) with D-Glucose

In order to find an alternative biosensor material which enables to detect the glucose level, therefore in this study, the interaction between Methacrylic Acid (MAA) based Molecularly Imprinted Polymer (MIP) with D-Glucose is investigated using the Density Functional Theory (DFT). The aim of this study is to determine whether a molecule of the MAA can be functioned as a bio-sensing of glucose. In this calculation, the Gaussian 09 with B3LYP and 631+G(d) basis sets is used to calculate all electronic properties. It is found that the interaction between a molecule of MAA and a molecule of D-Glucose was observed through the shortened distance between the two molecules. The binding energy of MAA/D-glucose and the Mulliken population analysis are investigated for checking possible interaction. From analysis, the MAA based MIP can be used as a bio-sensing material.