# Energy minimisation error for biphase

**URL:** <https://gromacs.bioexcel.eu/t/energy-minimisation-error-for-biphase/9631>\
**Category:** User discussions\
**Created:** [July 12, 2024, 10:10am UTC](https://gromacs.bioexcel.eu/t/energy-minimisation-error-for-biphase/9631 "2024-07-12T10:10:41Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![SP06](https://avatars.discourse-cdn.com/v4/letter/s/ecb155/32.png) [@SP06](https://gromacs.bioexcel.eu/u/SP06)\
**Post date:** [July 12, 2024, 10:10am UTC](https://gromacs.bioexcel.eu/t/energy-minimisation-error-for-biphase/9631/1 "2024-07-12T10:10:41Z")

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GROMACS version:  
GROMACS modification: Yes/No  
Here post your question : Energy minimisation gives following error for biphasic system(cyclohexane-water)-

Program: gmx mdrun, version 2021.4-Ubuntu-2021.4-2  
Source file: src/gromacs/domdec/domdec.cpp (line 2263)  
MPI rank: 0 (out of 20)

Fatal error:  
There is no domain decomposition for 16 ranks that is compatible with the  
given box and a minimum cell size of 4.86065 nm  
Change the number of ranks or mdrun option -rdd or -dds  
Look in the log file for details on the domain decomposition

I have attached my em.log file for reference.  
[em.log](https://gromacs.bioexcel.eu/uploads/short-url/fgDP8hg43mYFkjx1O44hIIb3BQT.log) (14.4 KB)  
Kindly help me to resolve this.

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<div class="post-metadata">

**Author:** ![SP06](https://avatars.discourse-cdn.com/v4/letter/s/ecb155/32.png) [@SP06](https://gromacs.bioexcel.eu/u/SP06)\
**Post date:** [July 12, 2024, 11:23am UTC](https://gromacs.bioexcel.eu/t/energy-minimisation-error-for-biphase/9631/2 "2024-07-12T11:23:49Z")

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I solved this using -ntmpi 1. But for some steps in between it showed one or more water molecules cannot be settled.

But after that I got the average potential energy as -  
9.43129e+06

 ![IMG_20240712_165123](https://europe1.discourse-cdn.com/flex017/uploads/bioexcel1/original/2X/0/0e75799328f6c94ad6a62c64eeef8bdd8219833d.jpeg)

my minim.mdp file-  
; LINES STARTING WITH ‘;’ ARE COMMENTS  
title = Minimization ; Title of run

; Parameters describing what to do, when to stop and what to save  
integrator = steep ; Algorithm (steep = steepest descent minimization)  
emtol = 1000.0 ; Stop minimization when the maximum force \< 10.0 kJ/mol  
emstep = 0.01 ; Energy step size  
nsteps = 50000 ; Maximum number of (minimization) steps to perform

; Parameters describing how to find the neighbors of each atom and how to calculate the interactions  
nstlist = 1 ; Frequency to update the neighbor list and long range forces  
cutoff-scheme = Verlet  
ns\_type = grid ; Method to determine neighbor list (simple, grid)  
rlist = 1.2 ; Cut-off for making neighbor list (short range forces)  
coulombtype = PME ; Treatment of long range electrostatic interactions  
rcoulomb = 1.2 ; long range electrostatic cut-off  
vdwtype = cutoff  
vdw-modifier = force-switch  
rvdw-switch = 1.0  
rvdw = 1.2 ; long range Van der Waals cut-off  
pbc = xyz ; Periodic Boundary Conditions  
DispCorr = no

Is my system energy minimized or is there some mistake here. I think it’s too high.