[gmx-users] Turn off the electrastatic interaction between 2 energy groups

[Uwe Richter]

Hi,

it's not totally clear to me what you want to do but you could subtract the
electrostatic interactions between the two groups afterwards. If the 
energy groups are defined properly the information is written in the
edr file, the final interaction energies also in the log file.

Uwe

> Hi all,
>      I already posted this question on the developer's list, but nobody 
> answers it. So I posted it here again. 
> 
>      Inomacs, "energygrp_excl" can exclude all non-bonded 
> interactions between pairs of energy groups. But I only want to 
> turn off the electrastatic interaction between 2 energy groups.
> 
>      The following is my idea. (I choose Cut-off for electrastatic 
> calculation and use grid for the neighbour searching.)
> 
>       There are 3 short range neighbour-lists generated in ns.c(vdw, 
> coup, vdwc). It seems to me that "vdwc" will store the information of 
> the 
> particls with both charges and the lj type. "vdw" will store the 
> information of the particles whose charge is 0, and "coup" will store 
> the information 
> of the particles whose lj is 0.(not sure?) What I have done is to loop 
> over the charge groups and judge if the 2 groups are  excluded, if they 
> are,
> I just add the particles in that group into "vdw" list instead of "vdwc" 
> list. Then it seems to me that only vdw interaction is computed even if 
> the 
> charge are not 0 for those particles.
>     But when I tested it, it did not work. Before I did the exclusion, 
> the elecstatic intereaction of the system is 0.16 kj/mol, but after I 
> chose the 
> exclusion, the elecstatic intereaction of the system is -201 kj/mol. It 
> seems that the 1-2, 1-3 neigbours are even computed. (My system includes 
> 
> 1 spc water molecule and 1 pf6 molecule).
>      Do you know what is wrong with my idea, and is there a better way 
> to do this?
> 
> Thank you very much!
> 
> Best
> Xuhui
>    
> 
> 
>   

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