Strange optimized geometry

[perfetti]

Dear Dr. Nordland,
        I really need your help.
        1) I used the structure.py you gave to me, and I got a straight line.
        2) I followed your recipe and moved the atoms at 1.5Angstrom, and then relaxed. And I got another straight line.
        
        The structure in your structure.py is not exactly 1.5Angstrom away from x,y, so I used both coordinates. However, both I got are straight lines. So I really don't know what to do next.
        I am attatching the scripts I used as well as the images I got.
        Plz give me some advice.Thanks.

[Nordland]

Okay I tried a couple of different things and ended up with the straight line and then I said to myself: What is the problem with this structure?

The bond between the two copper atoms must be stretched more than 20%, and therefore the normal FHI pseudo-potential is known for not being really super in the long range limit, and therefore I tried using the new HGH pseudo-potential and the tier 5 basis set.

And using the Copper basis set which is really excellent for Copper also in the long range, you can get the chain to snake like desired.

I am just redoing the calculation now, because I managed to delete the output, but you can have the input file.

[perfetti]

Thanks. Dear Dr. Nordland.
      This time the shape after relaxation seems better, however, there's no bond between Cu atoms. I tried to move one Cu atom almost 0.2 A closer to another Cu atom so they'll have bonds at first, but there's still no bonds after relaxation.
      The picture of relaxed structure is attatched.

[Nordland]

Allow me to quote myself

The bond between the two copper atoms must be stretched more than 20%, ....................

The bonds in VNL is purely visual, and if you open the properties window in the viewer, you can see that it will draw bonds between atoms that are within by default 0.5 to 1.1 of the covalent radius of other atoms. You can increase this maximum range, and if you increase it to 1.20 I think you will see the bonds between the copper atoms as well. Tune this parameter and you can get the plot you want

[perfetti]

Thanks, Dr. Nordland.
I really learned a lot from you.
Have a great weekend.