It is a one-dimensional ultrathin nanowire of gold atoms. I think the figure shows it's partly a covalent and ionic bond, which is not supposed to be.
Hello
Shambhu Bhandari chemical density plot shows the electrostatic potential i.e blue portion behave like electrophile and green behave like neutral and red behave like nucleophile during this processes ionic bond takes place.
Why would you expect bonds between atoms of the same type to be non-covalent? Each atom contributes approximately the same electron density to the space in between the atoms. Of course, the situation will be different at the ends of the chain.
Hi I do not understand why you said that the charge density plot suggests the bond is partly ionic. Your Au atoms in the chain are all equivalent. There are no reasons why a charge transfer between atoms will take place, and induce ionicity.
Also why do you think it is covalent (and not metallic, for instance) ?
Best,