I am working on a protonated polymer (~1000 atoms), where the Nitrogen atoms have a formal charge of +1 after protonation. I need dynamic charge reassignment (i.e. QEq), but traditional QEq falls short of correct charge assignment; a preferable option would be to use FC-QEq, where the charges are evaluated centered on a pre-assigned formal charge, at least at the first step. Since LAMMPS offers charge equilibration, is it possible to implement it here? Is a workaround with the available charge modules possible??
Thanks in advance.
What do you mean by “implement”?
What the capabilities of a LAMMPS version are is documented completely in its documentation. If a feature is not mentioned in the documentation it has not been programmed.
If you want to use a feature that is not available, you can get busy programming it in C++ yourself (LAMMPS is open source and many - if not most - of its features originate in users requiring something new and contributing their code), or find a collaborator that can do it, or submit a feature request (which will be added to a long list of requests, so don’t hold your breath).
P.S.:
You can assign an initial charge to atoms via a data file or the set command, but what comes out of that is a question of the QEq algorithm and the parameters used.
Thanks for your reply. I am not well-versed in C++, so I guess I have to do something else. One workaround might be modifying the electronegativity in the qeq params file to different values.