Browsing by Author "Musembi, Robinson"

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    First Principles Study of the Properties Of Cs2GaAgF 6 Double Halide Perovskite Compound for Optoelectronic and Thermoelectric Applications
    (Journal of Inorganic and Organometallic Polymers and Materials, 2025-05-01) Mbilo, Mwende; Musembi, Robinson; Kachira, John Peter; Nyamunga, Martin; Musanyi, Ibrahim; Wafula, Samuel; Yusuf, Madallah
    This study uses first-principles methods to analyze the structural, electronic, mechanical, thermophysical, optical, and ther- moelectric properties of the Cs 2GaAgF 6 double-halide perovskite compound. The results have revealed that the Cs2GaAgF 6 compound is mechanically and thermodynamically stable and can be potentially synthesized. The calculated band gap of the material was 2.27 eV, 2.41 eV, and 2.54 eV, derived from the local density approximation using Perdew–Zunger func- tional (LDA-PZ), the generalized gradient approximation using the Wu–Cohen (GGA-WC), and Perdew–Burke–Ernzerhof (GGA-PBE) functionals, respectively. The band gap was improved by using metaGGA functionals, which gave 3.10 eV, 3.15 eV, 3.15 eV, and 4.62 eV for strongly constrained and appropriately normed (SCAN), regularized strongly constrained and appropriately normed (rSCAN), restored-regularized strongly constrained and appropriately normed (r2SCAN), and Tran–Blaha-modified Becke–Johnson (TB-mBJ), respectively. The machine learning (ML) techniques predicted a band gap of 2.68 eV. The mechanical and elastic properties showed that the investigated compound is ductile and elastically anisotropic. Additionally, the optical properties showed excellent performance in the ultraviolet spectrum. Notably, the high absorption coefficients and optical conductivity values across the ultraviolet spectrum underscore the significant potential of the Cs 2GaAgF 6 double-halide perovskite compound for optoelectronic applications. Finally, the Cs 2GaAgF 6 double-halide perovskite compound showed a considerable figure of merit (ZT) value of 0.739 at approximately 600 K, suggesting its suitability for thermoelectric applications.
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    First Principles Study of the Properties of Cs2GaAgF6 Double Halide Perovskite Compound for Optoelectronic and Thermoelectric Applications
    (Journal of Inorganic and Organometallic Polymers and Materials, 2025-05-01) Mbilo,Mwende; Musembi, Robinson; Kachira, John Peter; Nyamunga, Martin; Musanyi, Ibrahim; Wafula, Samuel; Yusuf, Madallah
    . This study uses first-principles methods to analyze the structural, electronic, mechanical, thermophysical, optical, and thermoelectric properties of the Cs2GaAgF6 double-halide perovskite compound. The results have revealed that the Cs2GaAgF6 compound is mechanically and thermodynamically stable and can be potentially synthesized. The calculated band gap of the material was 2.27 eV, 2.41 eV, and 2.54 eV, derived from the local density approximation using Perdew–Zunger functional (LDA-PZ), the generalized gradient approximation using the Wu–Cohen (GGA-WC), and Perdew–Burke–Ernzerhof (GGA-PBE) functionals, respectively. The band gap was improved by using metaGGA functionals, which gave 3.10 eV, 3.15 eV, 3.15 eV, and 4.62 eV for strongly constrained and appropriately normed (SCAN), regularized strongly constrained and appropriately normed (rSCAN), restored-regularized strongly constrained and appropriately normed (r2SCAN), and Tran–Blaha-modified Becke–Johnson (TB-mBJ), respectively. The machine learning (ML) techniques predicted a band gap of 2.68 eV. The mechanical and elastic properties showed that the investigated compound is ductile and elastically anisotropic. Additionally, the optical properties showed excellent performance in the ultraviolet spectrum. Notably, the high absorption coefficients and optical conductivity values across the ultraviolet spectrum underscore the significant potential of the Cs2GaAgF6 double-halide perovskite compound for optoelectronic applications. Finally, the Cs2GaAgF6 double-halide perovskite compound showed a considerable figure of merit (ZT) value of 0.739 at approximately 600 K, suggesting its suitability for thermoelectric applications
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    First-Principles Study of the Structural, Electronic, Mechanical, and Optical Properties of Zintl-Phase K2AgBi Ternary Compound for Optoelectronic Applications.
    (2025-04-23) Kachira, John Peter; Musembi, Robinson; Nyongesa, Francis; Mbilo, Mwende; Nyamuga, Martin; Musanyi, Ibrahim
    A comprehensive first-principles study was conducted to explore the structural, electronic, mechanical, thermophysical, and optical proper ties of a Zintl-phase K2AgBi ternary semiconductor compound using density functional theory. The calculations employed the local density approximation (LDA), generalized gradient approximation (GGA), and meta-GGA methods. The computed negative formation energies proved the thermodynamic stability of the K2AgBi ternary compound. The computed bandgap values were 0.6732 and 0.7848 eV for the LDA and GGA, respectively. More refined bandgap estimates were obtained using meta-GGA methods, with the Tran–Blaha modified Becke–Johnson potential yielding 0.9346 eV and the revised strongly constrained and appropriately normed functional yielding 0.9778 eV. The projected density of states study revealed that the Ag3d, Bi2p, and K1s orbitals dominate the formation of the valence band, whereas the K4p, Ag2p, and K2s orbitals contribute significantly to the formation of the conduction band. Analysis of the mechanical properties confirmed that K2AgBi is mechanically stable and ductile. Optical analysis revealed strong absorption in the 1.0–15 eV energy range, high refractive index in the low-energy region, and distinct plasmonic response, suggesting potential applications in photovoltaics, optoelectronics, and plasmonic-based technologies.
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    Insights into the Optoelectronic and Thermoelectric Properties of Lead-Free Rb2NaIrF6 Double Perovskite Compound: A First-Principles Study
    (Elsevier B.V., 2025-07-01) Mbilo,Mwende; Musembi, Robinson; Kachira, John Peter; Onsate,Wisley Nyangau; Keheze, Fanuel Mugwanga; Mapasha, Refilwe Edwin
    This study investigated the structural, electronic, elastic, mechanical, thermodynamic, optical, and thermoelectric properties of the Rb2NaIrF6 lead-free double perovskite compound using first-principles methods. The structural stability of the perovskite was confirmed by the Goldschmidt tolerance and octahedral factors. Dynamic stability was confirmed through the negative energy of formation and positive frequency modes of the phonon dispersion curve. The dynamic stability results suggest that the studied compound could be potentially synthesised experimentally. The Rb2NaIrF6 compound is a direct semiconductor with electronic band gaps within the range of 2.14-3.76 eV, computed using different approximations. The mechanical stability was confirmed by the elastic calculation results. The Rb2NaIrF6 compound was found to be ductile, ionic, and anisotropic. The optical properties showed that Rb2NaIrF6 strongly absorbs light in the ultraviolet region, which is desirable for ultraviolet-photosensitive materials in optoelectronic devices. The computed thermoelectric figure of merit of the Rb2NaIrF6 compound is 0.81 at 1000 K, suggesting high thermoelectric efficiency. These findings demonstrate the potential of Rb2NaIrF6 lead-free double perovskite compound for optoelectronic and thermoelectric applications. Therefore, our investigation offers theoretical insights that can lead to the experimental synthesis and study of Rb2NaIrF6 lead-free double perovskites.