[gmx-users] Lincs all-bonds causing instability in otherwise stable system
Cara Kreck
cara.kreck at student.curtin.edu.au
Fri May 15 08:31:27 CEST 2015
I forgot to include an example of my mdp files. I've tried varying the timestep, running with and without pressure coupling, and obviously changing the constraints as outlined in the previous message:
integrator = md
dt = 0.001 ; 1fs
nsteps = 100000 ; 100ps
comm_grps = DOPC !DOPC
nstxout = 1000
nstvout = 0
nstlog = 1000
nstenergy = 1000
energygrps = DOPC !DOPC
nstcalcenergy = 5
nstlist = 5
ns_type = grid
pbc = xyz
rlist = 0.8
coulombtype = Reaction-Field
rcoulomb = 1.4
epsilon_rf = 62
vdwtype = Cut-off
rvdw = 1.4
tcoupl = berendsen
tc-grps = DOPC !DOPC
tau_t = 0.1 0.1
ref_t = 303 303
;Pcoupl = berendsen
;pcoupltype = semiisotropic
;tau_p = 1.0 1.0
;compressibility = 4.6e-5 4.6e-5
;ref_p = 1.0 1.0
gen_vel = no
constraints = all-bonds
constraint_algorithm = shake
continuation = yes
> From: cara.kreck at student.curtin.edu.au
> To: gromacs.org_gmx-users at maillist.sys.kth.se
> Date: Fri, 15 May 2015 14:17:28 +0800
> Subject: [gmx-users] FW: Lincs all-bonds causing instability in otherwise stable system
>
> Hi,
>
> I am having trouble constraining all-bonds with lincs in a system that is stable using shake all-bonds or lincs h-bonds in gromacs 4.6.7. The previous step using lincs h-bonds gave these energies:
>
> Step Time Lambda
> 200000 200.00000 0.00000
>
> Energies (kJ/mol)
> G96Bond G96Angle Proper Dih. Improper Dih. LJ-14
> 1.76317e+04 2.43132e+04 1.39308e+04 1.55159e+03 -2.91002e+03
> Coulomb-14 LJ (SR) LJ (LR) Coulomb (SR) Coulomb (LR)
> 4.07560e+05 -4.09017e+03 -1.26700e+04 -5.62217e+05 -3.06259e+03
> RF excl. Potential Kinetic En. Total Energy Temperature
> -1.24406e+05 -2.44368e+05 9.29185e+04 -1.51450e+05 3.02522e+02
> Pressure (bar) Constr. rmsd
> -1.98735e+02 1.95240e-06
>
> However, when I switch to lincs all-bonds the 0 step kinetic energy, temperature, and pressure are dramatically increased, even though continuation=yes and gen_vel=no. The system then quickly crashes. I tried using GMX_MAXCONSTRWARN=-1 and particle decomposition to get past the errors but then it simply stalls without crashing or outputting anything.
>
> Step Time Lambda
> 0 0.00000 0.00000
>
> Grid: 8 x 8 x 14 cells
> Energies (kJ/mol)
> G96Angle Proper Dih. Improper Dih. LJ-14 Coulomb-14
> 2.43132e+04 1.39308e+04 1.55159e+03 -2.91002e+03 4.07560e+05
> LJ (SR) LJ (LR) Coulomb (SR) Coulomb (LR) RF excl.
> -4.09017e+03 -1.26700e+04 -5.62217e+05 -3.06259e+03 -1.24406e+05
> Potential Kinetic En. Total Energy Temperature Pressure (bar)
> -2.62000e+05 4.92862e+05 2.30862e+05 1.93783e+03 1.04858e+04
> Constr. rmsd
> 1.44601e-02
>
> When I instead switch to shake all-bonds (with particle decomposition) I get a similar spike in the kinetic energy etc. but the system is able to recover without crashing. Unfortunately gromacs won't let me use pressure coupling with shake due to my twin-range cut-offs though, so I need to find a way to get lincs to work. I tried switching to lincs all-bonds after 100ps with shake all-bonds, and there was no longer the spike in energies except for the pressure:
>
> Step Time Lambda
> 100000 100.00000 0.00000
>
> Energies (kJ/mol)
> G96Angle Proper Dih. Improper Dih. LJ-14 Coulomb-14
> 2.46619e+04 1.38286e+04 1.50388e+03 -2.92380e+03 4.11368e+05
> LJ (SR) LJ (LR) Coulomb (SR) Coulomb (LR) RF excl.
> -3.50689e+03 -1.26695e+04 -5.64100e+05 -2.81505e+03 -1.24427e+05
> Potential Kinetic En. Total Energy Temperature Pressure (bar)
> -2.59079e+05 7.73473e+04 -1.81732e+05 3.04114e+02 -4.16208e+02
>
> Step Time Lambda
> 0 0.00000 0.00000
>
> Energies (kJ/mol)
> G96Angle Proper Dih. Improper Dih. LJ-14 Coulomb-14
> 2.46619e+04 1.38286e+04 1.50388e+03 -2.92380e+03 4.11368e+05
> LJ (SR) LJ (LR) Coulomb (SR) Coulomb (LR) RF excl.
> -3.50690e+03 -1.26695e+04 -5.64100e+05 -2.81533e+03 -1.24427e+05
> Potential Kinetic En. Total Energy Temperature Pressure (bar)
> -2.59079e+05 7.73979e+04 -1.81681e+05 3.04313e+02 5.61153e+02
> Constr. rmsd
> 2.45638e-04
>
> However, it still crashes with a domain decomposition error. When I switch back to particle decomposition it stalls again. I then tried decreasing the time-step to 0.1fs and I got lots of these errors before stalling:
>
> WARNING: Listed nonbonded interaction between particles 2485 and 2490
> at distance 3f which is larger than the table limit 3f nm.
>
> This is likely either a 1,4 interaction, or a listed interaction inside
> a smaller molecule you are decoupling during a free energy calculation.
> Since interactions at distances beyond the table cannot be computed,
> they are skipped until they are inside the table limit again. You will
> only see this message once, even if it occurs for several interactions.
>
> IMPORTANT: This should not happen in a stable simulation, so there is
> probably something wrong with your system. Only change the table-extension
> distance in the mdp file if you are really sure that is the reason.
>
> There were 156 inconsistent shifts. Check your topology
> There were 190 inconsistent shifts. Check your topology
>
>
> Whereas with domain decomposition and a 0.1 fs time-step it still crashes with a domain decomposition error. I don't understand why a system that is perfectly fine with lincs h-bonds and shake all-bonds can be so problematic with lincs all-bonds. Any suggestions?
>
> Thanks,
>
> Cara
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