I want to calculate the rdf between O3 atoms of different cholesterol molecules. Additionally, I want to avoid the calculation of rdf between the same molecule. How can I do this in gromacs ?
You will need to make an index file that has each of your cholesterol O3 atoms in a separate group. From there, it will simply be writing a script which to analyze all possible combinations, with you screening to remove undesired intra-cholesterol calculations.