A First-Principles Study of TiX 2 (X = S, Se, and Te) Compounds Optical Properties under the Effect of Externally Applie
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PTICAL PROPERTIES
A First-Principles Study of TiX2 (X = S, Se, and Te) Compounds Optical Properties under the Effect of Externally Applied Electric Field and Strain Aditya Dey* Department of Physics, Indian Institute of Technology Patna, Bihta Campus, Patna, Bihar, 801106 India *e-mail: [email protected] Received May 8, 2020; revised June 2, 2020; accepted June 3, 2020
Abstract—Optical properties of titanium dichalcogenide compounds, TiX2 (X = S, Se, and Te) have been calculated by first-principles calculations using density functional theory as implemented in SIESTA code. The unit cell of each of these compounds was optimized and the calculations were performed to obtain the optical properties. Further, external electric field (along Z direction) and biaxial strain (along X and Y directions) was employed to study their effect on these properties. The effect of biaxial strain on the geometry of the compounds is also studied. The optical properties are investigated for polarized light along the Z direction (c axis). This include the calculation of real and imaginary parts of dielectric function, absorption coefficient, reflectance, optical conductivity, and refractive index in 0–25 eV energy range. Various modulations of these properties are observed including the blue shifts and red shifts of energies with highest peaks in the visible region and also shifting of energies to other regions of the electromagnetic spectrum. Hence, due to the tunable diverse optical properties, the compounds can be useful in the field of optoelectronics and in making various optical devices. Keywords: density functional theory, electric field, biaxial strain, optical properties DOI: 10.1134/S1063783420100042
1. INTRODUCTION In recent studies of material science and related areas over a span of few years, two-dimensional materials are in the limelight due to their variety of properties and remarkable applications in numerous fields. Of these materials, potential research is being carried out on layered transition metal dichalcogenides (TDMC) because of its anisotropic physical properties and strong covalent-bound layers as well as their various technological applications [1–6]. The titanium dichalcogenide compounds, TiX2 (X = S, Se, and Te) are one of the types of TDMC that have attracted a great amount of attention due to their wide range of applications [7–13]. These compounds comprise covalently bonded Ti and X atoms in two-dimensional hexagonal planes. The planes are stacked together by chalcogen–chalcogen van der Waals interactions [14– 16]. These compounds have highly anisotropic physical properties. Therefore, significant changes in their properties can be made by foreign atoms or external factors. TiX2 crystallizes in 1T-type structure and with a space group P-3m1 at room temperature and pressure [17]. In earlier research works, these compounds have been studied both experimentally and theoretically
including the study on their various properties. With an emphasis on the theoretical studies of these compounds, many researcher
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