First-principles study of the structural and electronic properties of bulk ZnS and small ZnnSn nanoclusters in the framework of the DFT+U method

Abstract

We investigate the structural and electronic properties of bulk ZnS in zinc blende as well as in wurtzite phase, and ${\mathrm{Zn}}_{n}{\mathrm{S}}_{n}$ nanoclusters by using the Hubbard model $(\mathrm{DFT}+U)$. It provides an on-site Coulomb correction to mitigate some of the commonly known limitations of traditional DFT-GGA method such as the underestimation of band gap and inaccurate description of electronic band structure. Especially for the nanoclusters, the traditional DFT method cannot reproduce all properties accurately that are observed in the experiments. Within the framework of $\mathrm{DFT}+U$ method, our model is first able to predict various properties of bulk ZnS (zinc blende and wurtzite) as well as in nanoclusters with high accuracy. We empirically determined the Hubbard correction parameters ${U}_{d}$ and ${U}_{p}$ for $\mathrm{Zn}\text{\ensuremath{-}}3d$ and $\mathrm{S}\text{\ensuremath{-}}3p$ states, respectively, that could reproduce the measured values of band gaps, $d$-band positions, $p$-states bandwidths, lattice parameters, etc. with a reasonable agreement. It was found that our model can be compared very well with more accurate hybrid functionals at only a fraction of the computational cost. Further, the selected pair of ${U}_{d}$ and ${U}_{p}$ values are used to investigate the structural and electronic properties of ZnS nanoclusters and results agree well with the higher levels of theory.