Nick wrote:
Dear experts,

1- I am trying to get interaction energies between solute (3 chains A) and solvent 50 molecules B. In the index file I created two groups: one for all atoms of [A] and and [B] for all solvent molecules. and by setting A and B as energy groups in mdp file I am getting break down as A-A, A-B and B-B with g_energy.

I am a little confused as I dont know if I need to create different groups for my solute to get interaction energies A-A, A-B and B-B. I mean do I need to have [A1] for solute chain 1 ...[A3] for chain 3?


If you want a breakdown of per-chain energetics, then yes, specify each chain as a group. The programs will only do what you tell them, nothing more, nothing less.

and then sent A1, A2, A3 in mdp file and run g_energy? if I need to specify different chains, then to get say A-A should I average over all possible A1-A2, A1A3, A2-A3, A1-B, A2,B...? I am really confused ..


Theoretically, the short-range terms should sum, not average.

2- I know it is naive question but What does A1-A1 mean? How can one chain interact with itself?


Without knowing what the chain is, no one can answer this. Generally, any atoms that are within the short-range cutoff and further away than nrexcl bonds contribute to short-range interactions. Long-range interactions (i.e., PME terms) happen too, but you can't decompose that term with energygrps.

3- Do I need to use mdrun - rerun option to get beakdown or just g_energy gives what I need?


You need to -rerun. g_energy does not take an index file, and it only analyzes existing groups, it cannot derive new ones.

-Justin

Thanks for your help
Paniz


--
========================================

Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
MILES-IGERT Trainee
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin

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