# Simulation system collapses?

**URL:** <https://gromacs.bioexcel.eu/t/simulation-system-collapses/2606>\
**Category:** User discussions\
**Created:** [July 29, 2021, 1:47am UTC](https://gromacs.bioexcel.eu/t/simulation-system-collapses/2606 "2021-07-29T01:47:59Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![evali](https://avatars.discourse-cdn.com/v4/letter/e/eb9ed0/32.png) [@evali](https://gromacs.bioexcel.eu/u/evali)\
**Post date:** [July 29, 2021, 1:47am UTC](https://gromacs.bioexcel.eu/t/simulation-system-collapses/2606/1 "2021-07-29T01:47:59Z")

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GROMACS version: 2019.4

Hi all,

I was simulating a membrane-protein system. The system worked well after temperature and pressure equillibration (see the 1st picture). Then I tried to introduce an oscillating electric field to it. At the beginning, when the field amplitude was 0.5 V/nm, the system looked fine. However, when the field amplitude was promoted to 1.0 V/nm, the system collapsed as seen in the 2nd picture. I have tried to remove the pressure equillibration, but the system still collapsed. I am thinking the electric filed must bring something wrong. But I don’t know what is wrong. What should I do to avoid this issue? Does anyone have clues on this? Many thanks.

Below I have attached the parameter file where the field was added. The forcefield is amber14sb.

 ![original](https://europe1.discourse-cdn.com/flex017/uploads/bioexcel1/original/1X/566b88179924d252abe17ff5dfc6d5e300f28570.png)

define =  
integrator = md  
dt = 0.002 ; ps  
nsteps = 50000000 ;100 ns  
energygrps =  
nstcomm = 100  
comm\_mode = linear  
comm\_grps = DMPC D2R\_RIS Water\_and\_ions  
refcoord-scaling = com  
;  
nstxout = 0  
nstvout = 0  
nstfout = 0  
nstlog = 50000  
nstenergy = 50000  
nstxout-compressed = 5000  
compressed-x-grps = system  
;  
pbc = xyz  
cutoff-scheme = Verlet  
coulombtype = PME  
rcoulomb = 1.2  
vdwtype = cut-off  
rvdw = 1.2  
DispCorr = EnerPres  
;  
Tcoupl = V-rescale  
tau\_t = 0.2 0.2 0.2  
tc\_grps = DMPC D2R\_RIS Water\_and\_ions  
ref\_t = 303.15 303.15 303.15  
;  
gen\_vel = no  
gen\_temp = 303.15  
gen\_seed = -1  
; //// I have tried to use  
;Pcoupl = parrinello-rahman  
;pcoupltype = semiisotropic  
;tau\_p = 2.0  
;ref\_p = 1.0 1.0  
;compressibility = 4.5e-5 4.5e-5  
;  
freezegrps =  
freezedim =  
constraints = hbonds  
constraint\_algorithm = LINCS  
continuation = yes

electric\_field\_z = 1.0 25.1327 0 0

 ![collapse](https://europe1.discourse-cdn.com/flex017/uploads/bioexcel1/original/1X/62096a1131a95671ef1d00b32bc49e50c3a8f847.png)