Fadhlul Wafi Badrudin

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 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.

Establishment of Structural and Elastic Properties of Titanate Compounds Based on Pb, Sn and Ge by First-Principles Calculation

Structural, electronic, and optical properties of PbTiO3, SnTiO3, and GeTiO3 tetragonals (P4mm, 99 space group) were investigated using density functional theory as implemented in pseudo-potential plane wave in CASTEP computer code. The calculated equilibrium lattice parameter, electronic band structure, and optical properties for PbTiO3 (reference compound) are in good agreement with the available experiment data. The result also shows that GeTiO3 has a higher tetragonality (c/a=1.18) compared with SnTiO3 (c/a=1.15) and PbTiO3 (c/a=1.05). Calculations of the elastic constants of PbTiO3, SnTiO3, and GeTiO3 tetragonals show that they are mechanically stable. The electronic band structure shows that PbTiO3 has higher indirect band gap at X-G compared with SnTiO3 and GeTiO3, as explained in detail by the optical properties of ATiO3 (A=Pb, Sn, Ge) through the refractive index and absorption coefficient.

Comparative study of cubic Pm3m between SnZrO 3 and PbZrO 3 by first principles calculation

The properties of perovskite SnZrO3 (SZ) in cubic (Pm3m space group) was investigated via first principles calculation using the density functional theory (DFT) as implemented in CASTEP computer code. The lattice parameter of PbZrO3 (PZ) was calculated as a reference compound and the results show an accuracy values relative to the experimental values. In this first-principle calculations, the exchange-correlation functional is based on LDA-CAPZ which give underestimate in structural lattice parameters with typical errors of 2%. The elastic constants and their pressure dependence were calculated up to 30 GPa, and independent elastic constants (C11, C12, and C44), bulk modules, B are obtained and analyzed. Density of state (DOS) studies reveal that the anion O 2p, cation Sn 5p/Pb 5p and Zr 4d states of SZ and PZ play an important role which correspond to the top of valence states and bottom of conduction band. Meanwhile, direct band gap at X-X point is respectively obtained for both SZ and PZ along the higher symmetry direction in the Brillouin zone. The born effective charges (BEC) values of Sn and Zr (in SZ) have respectively been found to be +4.26 and +7.53. This is attributed to the bond charge response to the displacement caused by the strong covalency between cation orbital and O 2p. Results reveal anion O 2p, cation Sn 5p and Zr 4d states have also played an important role in optical transition in which they respectively correspond to the top of valence states and bottom of conduction band. The results of prototype SZ were compared and showed in good agreement with the calculated results of PZ.

Ab-initio study of active lone pair of Ge 2+ cation in novel perovskite GeTiO 3 compound

The effect of active lone pair Ge²⁺ in novel GeTiO<inf>3</inf> compound was investigated by ab-initio density functional theory (DFT) method as implemented in CASTEP computer code. In this work, the comparative of DFT study between novel GeTiO<inf>3</inf> compounds with lead-based PbTiO<inf>3</inf> compound have been carried out. From the calculation, we found that the corrected LSDA+U functional can improve and enhanced the electronic band gap of PbTiO<inf>3</inf> and GeTiO<inf>3</inf>. The band structure shows a large band gap in GeTiO<inf>3</inf> with 2.09 eV at the optimized U = 2 eV. The analysis of density of states (DOS) revealed strong hybridization between O 2p — Ti 3d states with additional hybridization of Ge 6p states. The significant of the contribution active lone pair is demonstrated by Ge 4s states located at about 7 eV. It shows similarity to DOS of the PbTiO<inf>3</inf> compound where the active lone pair contributed the large ferroelectric polarization in PbTiO<inf>3</inf>. The optical dielectric constants was also been investigated for further studies.