[gmx-developers] scaling 1-4 electrostatic interactions separately

[chris.neale at utoronto.ca]

Hello,

I am wondering why there is a [ pairtypes ] section only for LJ and  
not coulombic. I have been able to trick gromacs into properly  
combining two forcefields that have a different fudgeQQ, but that  
trick is fairly specific:
http://www.gromacs.org/pipermail/gmx-users/2006-September/023761.html

I am in the process of writing up the results of my protein-lipid  
simulations and I am currently trying to decide how to split the  
paper. I would like to split the method plus proof-of-concept section  
out into a simple one page methods letter but in that case I would  
need to convince the reader that the method that I have used is  
necessary and could not easily be replaced by a slight code  
modification to gromacs. In fact this may be the case and is the  
reason why I am writing to this list.

First: is there some important reason why a [ coulombic-pairtypes ]  
section could not exist, or is it just that nobody has dedicated a day  
of coding to make this happen? I figure that PME could make it more  
difficult, but don't really know.

Second: is gromacs 4.x likely to allow users to arbitrarily set  
coulombic 1-4 interactions in the same way that this can be done for  
LJ 1-4 interactions by [ pairtypes ] ?

I would like to emphasize that I am not asking anybody to do this.  
Rather, I would like to understand how easy it would be to do and how  
likely it is to be done since these answers will either motivate or  
undermine a simple methods letter of the type that I have mentioned.

Thanks,
Chris.