Mohamad Fariz Mohamad Taib

First Principles LDA+U Calculations for ZnO Materials

The electronic, structural, elastic, and optical properties of zinc oxide (ZnO) with wurtzite-type structure were investigated using first-principles calculation based on density functional theory (DFT) with local density approximation (LDA) plus Hubbard U (DFT–LDA+U)method. Hubbard U improved the calculated results, allowing it to exhibit good agreement with experimental data. The DFT–LDA+U method successfully predicted the electronic properties of ZnO with better described the localization of transition metal Zn 3d electron. The calculated optical dielectric function of ZnO and its relation with electronic properties were further discussed.

Structural, Electronic, and Lattice Dynamics of PbTiO3, SnTiO3, and SnZrO3: A Comparative First-Principles Study

The properties of cubic (Pm3m, 221 space group) perovskite prototypes PbTiO3 (PTO), SnTiO3 (STO), and SnZrO3 (SZO) were investigated via first-principles calculation using the density functional theory as implemented in CASTEP computer code. The lattice parameters of PbTiO3 (as the reference compound) were calculated. The accuracy values of the calculation functional (GGA-PBEsol) were acceptable relative to the experimental values with typical error of approximately 0.6% underestimate. The independent elastic constants (C11, C12, and C44) and bulk modulus, B, were obtained and analyzed. The density of state studies indicated hybridizations among anion O 2p, cation Pb 6s/Sn 5s and the Ti 3d/Zr 4d states of PTO, STO, and SZO. An indirect band gap was respectively obtained for both PTO and STO at the X-G point. A direct band gap was attained for SZO at the X-X point along the high-symmetry direction in the Brillouin zone. The born effective charge values of PTO, STO, and SZO were attributed to the responses of the bond charges to the displacement caused by the strong covalency between the cation orbital and O 2p (strong covalency A-O and B-O bonding). Results also reveal that anion O 2p, cation Pb 6s/Sn 5s, and Ti 3d/ Zr 4d states have played an important role in the instability of perovskite oxide. Comparative results from the PTO, STO, and SZO prototypes showed the calculated theoretical and experimental values were in good agreement.

Self-interaction corrected LDA + U investigations of BiFeO3 properties: plane-wave pseudopotential method

The structural, electronic, elastic, and optical properties of BiFeO3 were investigated using the first-principles calculation based on the local density approximation plus U (LDA + U) method in the frame of plane-wave pseudopotential density functional theory. The application of self-interaction corrected LDA + U method improved the accuracy of the calculated properties. Results of structural, electronic, elastic, and optical properties of BiFeO3, calculated using the LDA + U method were in good agreement with other calculation and experimental data; the optimized choice of on-site Coulomb repulsion U was 3 eV for the treatment of strong electronic localized Fe 3d electrons. Based on the calculated band structure and density of states, the on-site Coulomb repulsion U had a significant effect on the hybridized O 2p and Fe 3d states at the valence and the conduction band. Moreover, the elastic stiffness tensor, the longitudinal and shear wave velocities, bulk modulus, Poissons ratio, and the Debye temperature were calculated for U = 0, 3, and 6 eV. The elastic stiffness tensor, bulk modulus, sound velocities, and Debye temperature of BiFeO3 consistently decreased with the increase of the U value.

Electronic properties and gas adsorption behaviour of pristine, silicon-, and boron-doped (8, 0) single-walled carbon nanotube: A first principles study

Carbon nanotubes (CNTs) have received enormous attention due to their fascinating properties to be used in various applications including electronics, sensing, energy storage and conversion. The first principles calculations within density functional theory (DFT) have been carried out in order to investigate the structural, electronic and optical properties of un-doped and doped CNT nanostructures. O2, CO2, and CH3OH have been chosen as gas molecules to study the adsorption properties based on zigzag (8,0) SWCNTs. The results demonstrate that the adsorption of O2, CO2, and CH3OH gas molecules on pristine, Si-doped and B-doped SWCNTs are either physisorption or chemisorption. Moreover, the electronic properties indicating SWCNT shows significant improvement toward gas adsorption which provides the impact of selecting the best gas sensor materials towards detecting gas molecule. Therefore, these pristine, Si-, and B-doped SWCNTs can be considered to be very good potential candidates for sensing application.

Ab initio studies on the structural and electronic properties of bismuth ferrite based on ferroelectric hexagonal phase and paraelectric orthorhombic phase

The structural and electronic properties of bismuth ferrite (BFO) in ferroelectric hexagonal phase and paraelectric orthorhombic phase are investigated using ab initio density functional theory calculation. Calculations based on generalized gradient approximation GGA–PBEsol functional with semi-empirical Hubbard U method show good results for the structural and electronic localization of Fe 3d electrons and are consistent with experimental data. In addition, the calculated electronic band structure of BFO in paraelectric orthorhombic phase shows a smaller energy band gap than BFO in ferroelectric hexagonal phase. Thus, this calculation is consistent with the experimental data. The function of the stereochemically active lone pair of Bi 6s2 and chemical bonding of Fe‒O and Bi‒O on the structural instability of BFO are further elucidated in this study.

Determination of Electronic Structure and Band Gap of Li2MnP2O7 via First-Principle Study

The pyrochlore Li2MnP2O7 structure is an important new class of cathode for lithium ion batteries. First-principle calculations of ferromagnetic and antiferromagnetic (AFM) Li2MnP2O7 have been conducted within both the local density approximation (LDA) and the LDA+U frameworks. The optimized lattice parameters for AFM configuration calculated using the LDA+U scheme are closest and in good agreement with the experimental results. The electronic density of state analysis shows that Li2MnP2O7 is a charge-transfer insulator with a large band gap (4.183 eV) contributed between the O-2p and Mn-3d states, indicating that Li2MnP2O7 possesses poor electronic conductivity.

First-principles comparative study of the electronic and optical properties of tetragonal (P4mm) ATiO3 (A = Pb,Sn,Ge)

The structural, electronic, and optical properties of the special lone pair ferroelectric materials with tetragonal structures, namely, PbTiO3, SnTiO3, and GeTiO3 (P4mm, 99 space group), were investigated using density functional theory implemented in a pseudo-potential plane wave using the CASTEP computer code. The electronic properties indicated that hybridizations occur among anion O 2p, special lone pair (ns2), and the Ti 3d states. The complex dielectric constant was used to explain the comparison of optical properties of ATiO3 (A = Pb,Sn,Ge) relative to their electron transition from conduction to valence.

First-principles study on structural, electronic and optical properties of TiO2 for dye-sensitized solar cells photoanode

First-principles study based on density functional theory (DFT) framework for structural, electronic and optical properties of titanium dioxide (TiO2) in anatase and rutile phases are investigated. Anatase phase exhibits wide band gap compare to rutile phase. The partial and total density of states for TiO2 (anatase and rutile) describes the occupying of titanium (Ti) and oxygen (O) atoms at each energy level. TiO2 has a high dielectric constant to avoid the recombination process while its high refractive index provides the efficient of light diffusion. The optical absorption of TiO2 occurs in ultraviolet (UV) light of the wavelength photon. The results from the first-principles calculations will be helpful to give an understanding about the properties of TiO2 as promising photoanode in dye-sensitized solar cell (DSSC).

Study of Structural, Electronic and Optical Properties of Lanthanum Doped Perovskite PZT Using Density Functional Theory

Ferroelectric materials of lanthanum (La) doped PbZrTiO3 (PLZT) were investigated via first principles study. The structural, electronic and optical properties of PLZT in tetragonal structure (P4mm space group) were performed in the framework of density functional theory (DFT) with generalized gradient approximation (GGA) and local density approximation (LDA) methods. The calculated results of structural properties of PLZT were seen to be approximately close to the experimental data. The results of the electronic part were covered with the calculation of energy band gap and density of states (DOS). The highest valence band (VB) which lies at the Fermi level (EF) was dominated by the O 2p at F point. The conduction band (CB) of PLZT occurred at G point, which was primarily dominated by Ti 3d mixed at Pb and La p-state. Whereas the optical part was covered with the refractive index and absorption. The refractive index, n and the extinction coefficient, k were calculated with respect to photon energy. Those results obtained could be such a good prediction in studying parameters and properties of new materials.

First Principles Study on Structural and Electronic Properties of PZT and PSnZT Using Density Functional Theory

The geometry optimization of the tetragonal supercell 1x1x2 (P4mm, 99 space group) of PZT and PSnZT were calculated using different exchange correlation functional such as Local Density Approximate (LDA-CAPZ) and Generalized Gradient Approximation (GGA-PBE & GGA-PBEsol).The calculation using functional GGA-PBEsol exhibits the most accurate values of lattice parameter and volume of structure relative to the experiment results with typical error of approximately 1% underestimate (only for PZT-as reference materials). The electronic band structure and density of state (DOS) were also studied in order to understand the electron density and hybrization between cation and anion in the compound. The density of state studies indicated existing of hybridizations among anion O 2p, cation Pb 6s/Sn 5s (special lone pair) and the Ti 3d/Zr 4d states of PZT and PSnZT compound. An indirect band gap was respectively obtained for both cubic PZT and PSnZT at the F-G and Q-G point with 3.154 eV and 2.571 eV.