| ZnO is a semiconductor used extensively in varistor technology. The varistor is a variable resistor with high resistance at low voltage and low resistance at high voltage. In order to understand the nonlinear behavior of these devices, it is important to know the electronic structure of the semiconductor used. We use the linear muffin-tin orbital (LMTO) method to calculate the electronic structure of ZnO. In the calculation two empty spheres are incorporated into the ZnO unit cell to account for the large interstitial region, and the "d bands", which consist mostly of Zn 3d electrons, are also included. The results agree well with experiments and earlier works and give, for the first time, a complete band structure and densities of states starting from the first principle. We also develop the recursive Green's function-LMTO method which provides an efficient way of doing calculation in real space, a very important feature for many possible applications. A supercell of 120 atomic spheres are used as an example of this new technique. The construction of the supercell is discussed and the band structure of ZnO is recalculated with the new method. The results turn out to agree well with those done in k space. Finally we use the real space method to calculate the impurity states of Cr, Mn, and Co in ZnO host. Although our calculation is still preliminary, it agrees qualitatively well with earlier works. |
