# Calculate long-range electrostatic interaction using Reaction Field

**URL:** <https://gromacs.bioexcel.eu/t/calculate-long-range-electrostatic-interaction-using-reaction-field/515>\
**Category:** User discussions\
**Created:** [July 16, 2020, 6:45pm UTC](https://gromacs.bioexcel.eu/t/calculate-long-range-electrostatic-interaction-using-reaction-field/515 "2020-07-16T18:45:39Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![qvuvan](https://avatars.discourse-cdn.com/v4/letter/q/97f17d/32.png) [@qvuvan](https://gromacs.bioexcel.eu/u/qvuvan)\
**Post date:** [July 16, 2020, 6:45pm UTC](https://gromacs.bioexcel.eu/t/calculate-long-range-electrostatic-interaction-using-reaction-field/515/1 "2020-07-16T18:45:39Z")

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GROMACS version: 2018  
GROMACS modification: No

Dear all,  
I have performed a Steer molecular dynamics simulation, in which I fixed molecule A (named Rib in my system) and pull molecule B (Nascent in my system) away.  
During the simulation, I used the PME method for long-range electrostatics, now I want to calculate electrostatic interaction between molecule A and B (both long-range and short-range so I used Reaction Field to obtain long-range interaction as this paper mention: [https://pubs.acs.org/doi/abs/10.1021/acs.jcim.5b00012](https://pubs.acs.org/doi/abs/10.1021/acs.jcim.5b00012))

In the mdp file for interaction energy calculation:

> energygrps = Rib Nascent  
> coulombtype = Reaction-Field  
> rcoulomb = 1.2

This means that the interaction of atoms in molecules Rib and molecule Nascent will be treated as short-range interaction if the distance smaller than 1.2 nm, and long-range if larger than 1.2 nm.

When I use gmx energy to calculate interaction energy I got only these options:

> ```
> 1 Bond 2 Angle 3 Proper-Dih. 4 Improper-Dih. 
> 5 LJ-14 6 Coulomb-14 7 LJ-(SR) 8 Disper.-corr. 
> 9 Coulomb-(SR) 10 Position-Rest. 11 COM-Pull-En. 12 Potential     
> 13 Kinetic-En. 14 Total-Energy 15 Conserved-En. 16 Temperature   
> 17 Pres.-DC 18 Pressure 19 Constr.-rmsd 20 Vir-XX        
> 21 Vir-XY 22 Vir-XZ 23 Vir-YX 24 Vir-YY        
> 25 Vir-YZ 26 Vir-ZX 27 Vir-ZY 28 Vir-ZZ        
> 29 Pres-XX 30 Pres-XY 31 Pres-XZ 32 Pres-YX       
> 33 Pres-YY 34 Pres-YZ 35 Pres-ZX 36 Pres-ZY       
> 37 Pres-ZZ 38 #Surf*SurfTen                     
> 39 Coul-SR:Rib-Rib 40 LJ-SR:Rib-Rib                     
> 41 Coul-14:Rib-Rib 42 LJ-14:Rib-Rib                     
> 43 Coul-SR:Rib-Nascent 44 LJ-SR:Rib-Nascent                 
> 45 Coul-14:Rib-Nascent 46 LJ-14:Rib-Nascent                 
> 47 Coul-SR:Rib-rest 48 LJ-SR:Rib-rest                    
> 49 Coul-14:Rib-rest 50 LJ-14:Rib-rest                    
> 51 Coul-SR:Nascent-Nascent 52 LJ-SR:Nascent-Nascent             
> 53 Coul-14:Nascent-Nascent 54 LJ-14:Nascent-Nascent             
> 55 Coul-SR:Nascent-rest 56 LJ-SR:Nascent-rest                
> 57 Coul-14:Nascent-rest 58 LJ-14:Nascent-rest                
> 59 Coul-SR:rest-rest 60 LJ-SR:rest-rest                   
> 61 Coul-14:rest-rest 62 LJ-14:rest-rest                   
> 63 T-RNC 64 T-Water_and_ions     
> 
> ```

How can I obtain the long-range electrostatic interactions?  
Best regards,

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**Author:** ![jalemkul](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/jalemkul/32/18_2.png) [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)\
**Post date:** [July 17, 2020, 1:10am UTC](https://gromacs.bioexcel.eu/t/calculate-long-range-electrostatic-interaction-using-reaction-field/515/2 "2020-07-17T01:10:49Z")

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`energygrps` can only decompose short-range nonbonded forces.

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**Author:** ![qvuvan](https://avatars.discourse-cdn.com/v4/letter/q/97f17d/32.png) [@qvuvan](https://gromacs.bioexcel.eu/u/qvuvan)\
**Post date:** [July 17, 2020, 8:26am UTC](https://gromacs.bioexcel.eu/t/calculate-long-range-electrostatic-interaction-using-reaction-field/515/3 "2020-07-17T08:26:40Z")

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Dear Justin,  
So how can I get the long-range electrostatic interactions?  
Best regards,  
Quyen

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**Author:** ![jalemkul](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/jalemkul/32/18_2.png) [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)\
**Post date:** [July 17, 2020, 11:11am UTC](https://gromacs.bioexcel.eu/t/calculate-long-range-electrostatic-interaction-using-reaction-field/515/4 "2020-07-17T11:11:43Z")

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I don’t know of a way to calculate those energies.

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<div class="post-metadata">

**Author:** ![qvuvan](https://avatars.discourse-cdn.com/v4/letter/q/97f17d/32.png) [@qvuvan](https://gromacs.bioexcel.eu/u/qvuvan)\
**Post date:** [July 17, 2020, 11:12am UTC](https://gromacs.bioexcel.eu/t/calculate-long-range-electrostatic-interaction-using-reaction-field/515/5 "2020-07-17T11:12:39Z")

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Thanks, Justin