In the implementations of DFT using Gaussian basis sets, it is common to set the net charge. What exactly does this do? The Gaussian (program) manual, for instance, says that it introduces a background charge distribution made of point particles. This raises more questions than it answers for me.

1) If it's made of point particles (presumably at some internally defined coordinates), how is it a background charge distribution?

2) What exactly does setting the charge do? Is it just adjusting the electronic energy? Does it impact the geometry optimizations or the spin states given a pre-specified spin multiplciity?

I'm having trouble understanding what the charge is actually doing in terms of the DFT calculation itself. It's not a setting in plane-wave calculations, so the parallels are not clear to me.

  • $\begingroup$ The Gaussian manual (or whatever that is) cites 2 articles. Did you read them? $\endgroup$ – Raditz_35 Dec 13 '17 at 5:59
  • $\begingroup$ Wow, I didn't see that. Apologies. I'll read them now that I know where to look. $\endgroup$ – Argon Dec 13 '17 at 6:06
  • $\begingroup$ The keyword has absolutely nothing to do with DFT, that is just what they use in the example. $\endgroup$ – Martin - マーチン Dec 13 '17 at 6:13
  • $\begingroup$ Thanks, Martin. I'll check out the papers to learn more about what's going on. Good to know it's not related to the DFT implementation. $\endgroup$ – Argon Dec 13 '17 at 6:16
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    $\begingroup$ You can use it to add point charges to your calculation and see how that effects the energy, etc. I have never used it before, and that's only what I take home from the explanation in the manual. I would say, for everyday use it is not worth knowing. $\endgroup$ – Martin - マーチン Dec 13 '17 at 6:29

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