I am not really sure that calculated conormer is global minimum, but that is rather secondary, while almost no individual conformer will be symmetrical and have 0 dipole. (under "symmetrical" i mean in this case presence of "symmetry through the origin" - Ci, D2 and more complex point groups). Nevertheless averagely over ansamble (including full set of enantio- and diastereo-mers) rgat should have 0 dipole.

interested

This might be helpful. I got the structure of this compound from its crystal structure (10.1126/sciadv.1501491). You can try starting your optimizations from this structure, but I'm not sure if you can get 0 dipole moment in a optimized structure as big as this one (not a simple task I think), since small asymmetries in stable conformers can induce a dipole moment.

Thanks Dmitry Sharapa and the report (doi:10.1038/s41528-017-0002-0) says that this molecule has zero dipole. But I am not getting that value while i do the calculation. I wonder about that.

Thank you Eduardo Maurina Morais. I referred the article which you suggested already. But, yes as you mentioned i am not getting 0 dipole moment, even i tried nearly 5 times.

If you look in Table S1 in supplementary of the paper you will see that crystal structure orientation has nonzero dipole. It turns into zero only for some "ideal" structure, coordinates of which are not provided. One can try to build such a symmetric conformer (also i would guess it may has lower repulsion between MeOPh- fragments), based most likely on xyz provided by Dr. Morais, by further turn of a fragment based on N36-nitrogen. My guess is that when on the topview molecule would look like propeller, one might have good noncovalent interaction and low dipole (things are generallz independent). However that is just my guess.

And once again - if one conformer (even global minimum) has 0 dipole, this does not mean that all other or any other conformer will be like that.

Thank you Dr. Dmitry Sharapa. I have see that table S1. My query is how to draw such ideal structure for this molecule and estimate the DFT to attain 0 dipole. And I am unable to open Dr.Morais's file (.xyz). Even, today i tried again to estimate the DFT and this time I am getting more than 3 dipole and the HOMO and LUMO diagrams are worse than earlier.

I agree with Mr.Eduardo Maurina Morais, a small asymmetries in stable conformers can induce a dipole moment, as well as the gas phase of computed structure by DFT. may need to try with appropriate basis set.

Mr. Somasundaram, I had no problem opening the files in Gabedit and Avogadro, this xyz file, but since the structure is not positioned close to the origin, it may be an issue. Try opening this one attached to this answer. And about the comments of Mr. Dmitry Sharapa, he is absolutely correct, and I really find hard to believe that they found a 0 dipole moment conformer, and there is no way of checking this claim, since they didn't provide the XYZ file for it. Also, the structure I'm providing is a crystal structure, which does not represent the structure in the gas phase, but It can serve as a good starting point. And in regards to the HOMO/LUMO energies, they used ωB97X-D/6-31 G**, and you are using B3LYP/6-31 G, which will result in different energies.

Thanks you Mr. Eduardo Maurina Morais. Actually I was trying to opening this xzy file in gaussian. I don't have Gabedit and Avogadro. As both of you said, I too hardly believe about that 0 dipole what they mentioned in that article. And I too used ωB97X-D/6-31 G** but it is still running not yet completed. Can you please tell me what does mean that ** functions and where can i find it in gaussian. is that same ++?

You should be able to open the file Spiro-OMeTAD(2).xyz on gaussian, and if for some reason you can't, you can download Avogadro and Gabedit for free. Regarding the * and + symbols, they don't represent the same thing, * means that the basis set has polarization functions on heavy atoms, ** means it has polarization functions on heavy atoms and hydrogen. The + symbol means that the basis set has diffuse functions on heavy atoms, and ++ means that the basis set has diffuse functions on heavy atoms and hydrogen. If you want more details on what this means, a quick google search on polarization and diffuse functions should be enough, but you will find more details in computational chemistry books. This notation is only valid for Pople basis sets, other families of basis sets have different notations.

Thanks Mr. Eduardo Maurina Morais. I will try to download those programmings. I understand about the * and + symbols. Thanks again. could you please let me know where can I find the */** functions in gaussian. Because when I choose 6-31G, it doesn't appear. But many articles says that they run the calculation with 6-31G** functions. It appears some other functions like 3-21G but not for 6-31G. So, can you please help me on this?

6-31G* = 6-31G(d) and 6-31G** = 6-31G(d,p)

Oh my god. actually I keep that while we run. but I didn't aware that. thank you so much Mr. Morais. You made my day.