First-principles study on the electronic structure of Ti-doped NbSe2

Layered transition metal dichalcogenides (LTMDs) have renewed interest as electronic materials, but the poor conductivities hinder their further development. Chemical doping can often significantly modify atomic structures and electronic functionalities of a wide range of materials and thus acts as one of the most effective ways to precisely tune material properties for technological application. Here, the geometries and band structures as well as the densities of states of pure NbSe2 and Ti-doped NbSe2 nanostructure are studied by employing the ab-initio plane-wave ultra-soft pseudo potential technique based on the density functional theory. We optimize the ground state of NbSe2 in the layered structure by using the generalized gradient approximation for the exchange-correlation potential. The computational structural parameters are in good agreement with experimental values within 2.5%. To investigate the stability of the doped system with changing the concentration of Ti atoms, 2 x 2 x 12H-NbSe2 supercells are taken into consideration. Meanwhile, we consider a total of three possible Ti-doping models: substitution, intercalation, and embedded model, and investigate the energy band diagrams, state densities and densities of partial wave state diagram before and after the doping. The results show that the energy electron density of states reaches a higher peak, and the band structure near Fermi level (E-F) is changed obviously, resulting in the variations of the band gap and E-F position and then the increase of electronic conductivity after doping. In addition, our calculations also predict that the electron transport properties can be enhanced by doping Ti and it can be regarded as a useful way to tailor electronic states so as to improve electron transport properties of 2H-NbSe2. Such a remarkable modification of electronic structure of 2H-NbSe2 by chemical doping offers an additional way of modulating performances of LTMDs and developing new electrical contact composite materials.