Electric field

It is possible to apply a uniform external electric field given by a sawtooth waveform during the SCF calculation and the geometry optimization. For example, an electric field of 1.0 GV/m (10$^9$ V/m) is applied along the a-axis, in your input file specify the keyword 'scf.Electric.Field' as follows:

     scf.Electric.Field   1.0 0.0 0.0   # default=0.0 0.0 0.0 (GV/m)

The sign of electric field is taken as that applied to electrons. If the uniform external electric field is applied to a periodic bulk system without vacuum region, discontinuities of the potential are introduced, which could cause numerical instabilities. On the other hand, for molecular systems, the discontinuities are located in the vacuum region, indicating that numerical instabilities may not be induced.

As an illustration of the electric field, changes of total charge in a nitrobenzene molecule induced by the electric field are shown in Fig. 22. We can see that a large charge transfer takes place among oxygens in -NO$_2$, para-carbon atom, and para-hydrogen atom. The input file is Nitro_Benzene.dat in the directory 'work'. See also Section 'Analysis of difference in two Gaussian cube files' as for the difference charge maps shown in Fig. 22.

Figure: Difference in the total charge density of a nitrobenzene molecule between the zero-bias voltage and (a) 10 GV/m, and (b) -10 GV/m of applied bias along the a-axis, where orange and blue colors mean the increase and decrease of charge density. Tilted arrows depict the slope of applied electric fields. The contour maps were drawn using a software, gOpenMol [48]. The input file is Nitro_Benzene.dat in the directory 'work'.