How to complete the missing atoms on the surface of Fe3O4 spherical cluster model?

Hi Everyone,

I have a problem. I want to build a spherical cluster model of Fe3O4 with a diameter of 2.5nm.But after I took the size, there was a problem in the structure. I wanted them to have their own complete coordination atoms (Fe atom coordinated with O, O coordinated with H, and the final charge of the system was 0).But after I took the size, there were problems in the structure. The atoms in the outer ring could not meet the requirements, so they were directly cut off. Could you please tell me what I should do?

Any help would be appreciated.

Thank you.

Jiang.