M. K. Yaakob

Effect of pressure on structural, electronic and elastic properties of cubic (Pm3m) SnTiO 3 using first principle calculation

The electronic band structure, density of state and elastic properties of lead-free perovskite oxide SnTiO3 (ST) were investigated by employing first principles calculation using the Density Functional Theory (DFT) within local density approximation (LDA). The energy band gap was calculated from the separation between the Ti 3d (conduction band) and the maximum of O 2p (valence band). This gives an indirect band gap of 2.36 eV. The elastic constants and their pressure dependence were calculated up to 30 GPa and the independent elastic constants (C11, C12, and C44), bulk modules, B were obtained and analyzed. The results showed that SnTiO3 have a mechanical stability in cubic phase (Pm3m).

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.

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 Principle Study of Dynamical Properties of a New Perovskite Material Based on GeTiO3

The dynamical properties of a new perovskite GeTiO3 materials have been investigated by using first principle calculation based on Density Functional Theory (DFT) within the gradient generalized approximation (GGA). All calculations were performed using the Cambridge Serial Total Energy Package (CASTEP) computer code. The calculations include the structural parameter, Born effective charges, and phonon dispersion. The calculated Born effective charges and phonon dispersion have been analyzed and the possibility of ferroelectric feature in GeTiO3 compounds has been discussed. From the analysis, the calculated Born effective charge ZGe and ZTi showed large anomaly compared to the nominal charge which contributed to the large atomic displacement. The calculated phonon dispersion showed the most unstable mode was at G point and the unstable modes were dominated by Ge branch. The dynamical properties and ferroelectric properties in GeTiO3 are discussed and compared with the ferroelectric feature in PbTiO3.

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).

First Principles Calculation of Tetragonal (P4 mm) Pb-free Ferroelectric Oxide of SnTiO3

The properties of tetragonal (P4 mm, 99 space group) SnTiO3 were investigated via first-principles implemented in CASTEP computer code. The calculation of formation energy shows that the tetragonal P4 mm with the lowest energy optimization is at the ground state equilibrium structure compared to the ilmenite structure. The result also shows that SnTiO3 has a higher tetragonality (c/a = 1.18). Moreover, the elastic constant of SnTiO3 also confirmed that this compound has the tetragonal phase with a good mechanical stability. The electronic properties also indicated that the hybridizations occur among anion O 2p, cation Sn 5s and the Ti 3d states with an indirect band gap at the X-G point. The optical properties of SnTiO3 were determined by the complex dielectric constant and refractive index and they were compared to PbTiO3.