Can lammps do this?

Dear Xiaohui,

As Axel said, you have several choices. You can try to construct your total simulation

box with Moltemplate. I do not know what the lattice of your metal is, anyway If you are

familiar with crystallography you can build the structure of your metal

and then add your water molecules to it with Moltemplate.

You have to read the data file first, then use the create_atoms command
to add the metal atoms.

and for that approach you also need increase the number of atom
types listed in the data file so that it contains room for any
additional atom types added later through create_atoms