Simulation of Transition Metal Dichalcogenides

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The discovery of graphene in 2004 by Konstantin Novoselov and Andre Geim opened a new scientific arena: “2D materials”. The finding of new layered and non-layered materials and their potential applications in various fields has been taken a great attention in recent years. A wide variety of 2D materials such as transition metal dichalcogenides (TMDs), transition metal trichalogenides (Bi2Se3, Bi2Te3, etc.), transition metal monochalcogenide (GaSe, GaS, etc.), transition metal thiophosphides (MnPS3, FePS3, etc.), silicene, phosphorene and hexagonal boron nitride have been found to possess many fascinating and unique properties that are promising for various potential applications such as in optoelectronics, sensors, spintronics, valleytronics, energy storage and catalysis. Among the 2D family, the TMDs grasp diverse properties, ranging from insulator, semimetal, metal, semiconductor and superconductor and make them most interesting 2D materials in both academic and industrial perspectives. The TMDs are usually abbreviated by the chemical formula of MX2, where M is a transition metal such as Cr, Mo, W, Re, Ta, Zr and Pd, and X is a chalcogen of S, Se and Te. The different filling states of the d orbitals in this wide range of transition metals gives rise to TMDs with versatile properties. Among TMDs, group 6 TMDs such as MoS2, WS2, MoSe2 and WSe2 are attracting great attention due to their semiconducting nature, layer-dependent bandgap and strong light–matter interaction. The finite and tunable bandgap of group 6 TMDs compensate the lack in microelectronic application of graphene which arises due to its gapless feature. Herein we address different phases of TMDs including hexagonal (H), trigonal (T) and rhombohedral (R). We reviewed the optical and electronic properties such as thickness-dependent band structure, spin–orbit coupling, excitonic properties, Berry-phase-related properties and valley Hall effect of semiconducting TMDs. The modulation of electronic properties by external stimuli such as electric field and strain is also discussed in this chapter. The metallic TMDs such as 1T phase of group 6 TMDs, Ti-, V-, Nb-based TMD and 2H phase of NbS2, NbSe2, TaS2 and TaSe2 are discussed. The magnetism, strain and doping-induced magnetism in both metallic and semiconducting TMDs are addressed in this chapter.