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BiOI is reported to be a promising photocatalytic material for splitting water and decomposing pollutants in the visible range. However, previous investigations focus mainly on its photocatalytic property and other properties are not well studied. Here we put our effort to study the electronic, elastic and vibrational properties of BiOI. The results indicate that BiOI is an indirect narrow band gap semiconductor. Bi–O bonds have both covalent and ionic characteristics while Bi–I bonds may have more ionic nature. BiOI is mechanically and dynamically stable. However, calculated directional bulk and Young's moduli reveal that it is seriously mechanically anisotropic, originating from its layered structure. Its infrared absorption spectrum is simulated and four peaks are found. The origins of these peaks are explored based on the calculated Born effective charges and vibrational eigenvectors at the Brillouin zone center. In addition, the dielectric constants of BiOI are computed and discussed. We hope our study will enrich the knowledge of BiOI and other similar materials. • Bonding property within BiOI is studied by comprehensive methods. • Elastic properties of BiOI are investigated and detailedly analyzed. • Infrared absorption spectrum of BiOI is simulated and its origin is explored. [ABSTRACT FROM AUTHOR]

LiZnPS 4 is thought to be a promising mid-infrared optical crystal and lithium battery material, but its fundamental properties are still not well investigated. In this work, we performed a systematic study on its electronic, elastic, infrared and electrical properties. The results indicate that LiZnPS 4 is an indirect band gap crystal. Calculated partial density of states reveals that the top of its valence band is formed by the S 3p orbital while the component of the bottom of the conduction band is complex. The Zn 4p orbital is not empty in LiZnPS 4 owing to the tetrahedral coordination of the Zn atoms. Calculated elastic properties indicate that LiZnPS 4 is a mechanically stable crystal with elastic anisotropy. It has a relatively low Debye temperature of 294.8 K. Its infrared absorption spectrum was simulated and the origins of the strong peaks in it were revealed. Vibrational modes at the Brillouin zone center were illustrated and Born effective charges were calculated and discussed. Computed dielectric constants uncover that electrons contribute more to the total dielectric constants than ions. Studies imply that LiZnPS 4 –Li+ battery has a high theoretical voltage, a low electric capacity and a slightly high activation barrier. • Zn 4p orbital is found to be partly occupied for the special bonding pattern. • Infrared absorption spectrum is simulated and the related properties are studied. • Electrical properties of LiZnPS 4 are studied for possible use in lithium battery. [ABSTRACT FROM AUTHOR]

KBaBi is predicted to be a topological insulator recently, but most fundamental properties of it have not been studied. In this work, first-principles calculations were carried out to study its electronic, bonding, elastic, vibrational and dielectric properties. The results indicate that KBaBi has a band gap of 0.22 eV with the presence of spin orbital coupling. Weak p-d hybridization exists between the Ba 5d and the Bi 6p orbitals, so KBaBi has some covalent property, as revealed by the electron density difference. Studies imply that KBaBi is mechanically and dynamically stable, but it is mechanically anisotropic. KBaBi has a theoretical bulk modulus of 20.8 GPa and a shear modulus of 11.7 GPa. Group theory analysis indicates that there are six infrared- and four Raman-active modes at the Brillouin zone center of KBaBi. The vibrational frequencies and the corresponding eigenvectors were calculated and discussed. Calculation unveils that the electrons have more dielectric contribution to the total dielectric constants than the ions in the ab plane, but it is revised along the c axis. Investigations of the band structure, the Debye temperature and the phonon dispersion curves indicate that KBaBi is a promising thermalelectric material. Calculations indicate that KBaBi is metallic without SOC, but is an insulator with SOC. Theoretical studies reveal that KBaBi is mechanically and dynamically stable, Ba 5d orbital plays an important role in forming the crystal and KBaBi may be a promising thermalelectric material. Image 1 [ABSTRACT FROM AUTHOR]

In 2 Se 3 is an important compound having a complex phase diagram. In this work, we found a non-layered phase of In 2 Se 3 with the help of the particle swarm optimization method. Studies indicate that this phase is dynamically stable. It is an indirect band gap semiconductor with a gap of 2.36 eV. Calculated elastic constants imply that it is mechanically stable with elastic anisotropy. It has a low bulk modulus and Debye temperature despite of its non-layered structure. There are five strong peaks in the simulated infrared absorption spectrum and the corresponding vibrational modes are presented. Born effective charges and dielectric constants are obtained and discussed. The computed birefringence indicates that it might be a potential nonlinear optical crystal. • A non-layered In 2 Se 3 with dynamical and mechanical stability is predicted. • It is an indirect band gap semiconductor formed by Se-linked tetrahedrons. • Computed birefringence indicates its possible use as nonlinear optical crystal. [ABSTRACT FROM AUTHOR]