Charge doping

The following keyword is available for both the electron and hole dopings.

    scf.system.charge     1.0     # default=0.0
The plus and minus signs correspond to hole and electron dopings, respectively. A partial charge doping is also possible. The excess charge given by the keyword 'scf.system.charge' is compensated by a uniform background opposite charge, since FFT is used to solve Poisson's equation in OpenMX. Therefore, if you compare the total energy between different charged states, a careful treatment is required, because additional electrostatic interactions induced by the background charge are included in the total energy. Note that in Sec. 58, a proper way of treating charged and isolated systems is discussed.

As an example, we show spin densities of hole doped, neutral, and electron doped (5,5) carbon nanotubes with a finite length of 14 Å in Fig. 29. The neutral and electron doped nanotubes possess the total spin moment of 1.0 and 2.2, while the total spin moment almost disappears in the hole doped nanotube. We can see that the spin polarization takes place at the edges of the neutral and electron doped nanotubes due to dangling bonds of edge regions.

Figure 29: Spin densities of (a) four hole doped, (b) neutral, and (c) four electron doped (5,5) carbon nanotubes with a finite length of 14 Å. The input file is 'Doped_NT.dat' in the directory 'work'.