# Orbital Visualization from Gaussian .fchk

#1

Hello, I am a graduate school student of organic chemistry.
I recently knew Avogadro, and was really amazed how this software is awesome.

I have a question about the visualization process of molecular orbitals.
When I open a Gaussian .fchk file (which generated from a .chk file by formchk command of Gaussian 09) by Avogadro, I was surprised that I can quickly access visualized molecular orbitals, because it took much longer time for visualizing molecular orbitals when I used GaussView 5 (MO Editor) or Gaussian cubegen command (for example, "cubegen 0 MO=homo example.fchk example.cube ").

Therefore, my question is as follows.
・Where the visualized surfaces of molecular orbitals came from ?
Avogadro program calculated them ? or they were originally included in .fchk file ?
・ Are the visualized surfaces equivalent to those calculated by Gaussian cubegen command ?

I sincerely appreciate staff members for preparing such a warm community, and apologize my unfamiliar English and newbie questions.

#2

Avogadro will pre-generate MO orbital surfaces from .fchk files and similar computational results.

The .fchk file does not contain the surfaces - only the orbital coefficients and basis set information needed to generate them.

I don’t know if the defaults of Avogadro and Gaussian cubegen are exactly the same, but yes, the orbitals are equivalent.

(In general, Avogadro will use multiple cores on your computer to generate surfaces, so it is often faster than cubegen. I haven’t used GaussView in ages, but unless it uses multiple cores, it will also be slower.)

#3