Radial distribution function (RDF) for pairs having same atom types

Dear all,

I have a system containing a water-oil emulsion layer placed on top of a membrane. And I want to compute the radial distribution function (RDF) of the oil from the membrane. My system has 6 atoms types in total:

#1 12.0107 # C

#2 18.9984 # F

#3 1.00794 # H

#4 14.0067 # N

#5 15.9994 # O

#6 47.867 # Ti

The oil has atom types #1 and #3
Membrane has all atom types

To compute the RDF for the pair of oil-membrane I set:

compute 1 all rdf 100 2 1

(atomtype #2 as central atom type (of the membrane), while atom type #1 (or #3) as distribution atom type (of the oil))

Since both the membrane and the oil have atom types #1 and #3, how to modify my above command so that LAMMPS can distinguish which atom types are from the membrane and which ones are from the oil.

Thank you.

Kind regards
Tan Vu Bui

Just set your system up in such a way, that the atoms with the same force field parameters in the two different kinds of molecules have different numeric atom types in the data file. then there is no more problem.