# Analysis energy vdw and coulomb electrostatic for protein

**URL:** https://gromacs.bioexcel.eu/t/analysis-energy-vdw-and-coulomb-electrostatic-for-protein/5756
**Category:** User discussions
**Tags:** mdrun, analysis-tools
**Created:** [February 8, 2023, 2:29pm UTC](https://gromacs.bioexcel.eu/t/analysis-energy-vdw-and-coulomb-electrostatic-for-protein/5756 "2023-02-08T14:29:02Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![vader](https://avatars.discourse-cdn.com/v4/letter/v/9d8465/32.png) [@vader](https://gromacs.bioexcel.eu/u/vader)
#### Post date: [February 8, 2023, 2:29pm UTC](https://gromacs.bioexcel.eu/t/analysis-energy-vdw-and-coulomb-electrostatic-for-protein/5756/1 "2023-02-08T14:29:02Z")

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Hi,

I’m totally beginner in Gromacs, but I’m trying calculation VDW and electrostatic energy for protein in water.  
After MD simulation I got the following data such as:  
Coul-14:Protein-Protein 48723.9 – 52.5646 128.039 (kJ/mol)  
LJ-14:Protein-Protein 2911.89 – 63.8298 -132.528 (kJ/mol)

Then I tried calculation these interaction by using option: Coul-SR:Protein-Protein and LJ-SR:Protein-Protein and I get the following data:  
Coul-SR:Protein-Protein -70583.7 – 202.553 390.266 (kJ/mol)  
LJ-SR:Protein-Protein 300.207 – 150.764 -255.735 (kJ/mol)

Which of these values ​​look correct ? I want calculate vdw and electrostatic interactions only for protein.  
What can be indicated by a high positive and high negative impact value for electrostatic interaction ? Whether the interactions in the protein are strongly attractive or repulsive? My another question is related with “Tot-Drift” - how I can interpreting this parameter ?

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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: [February 9, 2023, 6:37pm UTC](https://gromacs.bioexcel.eu/t/analysis-energy-vdw-and-coulomb-electrostatic-for-protein/5756/2 "2023-02-09T18:37:33Z")

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> [@vader](#):
>
> Which of these values ​​look correct ? I want calculate vdw and electrostatic interactions only for protein.  
> What can be indicated by a high positive and high negative impact value for electrostatic interaction ?

Decomposing interaction energies into the various components is physically meaningless. No force field is parametrized to give a sensible answer here (because there are no target data that can be used for parameter fitting). The sum of the interaction energy components _may_ be meaningful, but only if the force field explicitly targets these quantities (e.g. CHARMM).