[gmx-users] MTTK with double precision GROMACS

[khaos]

Dear all,

I'm trying to run the DPPC bilayer simulation using the double precision
GROMACS with the MTTK pressure coupling method.
However, I've got an error like this:

-------------------------------------------------------
Program mdrun_d, VERSION 4.6.5
Source code file:
/users/khaos/prog/src/gromacs-4.6.5/src/mdlib/iteratedconstraints.c, line:
226

Fatal error:
Could not converge NPT constraints

For more information and tips for troubleshooting, please check the GROMACS
website at http://www.gromacs.org/Documentation/Errors
-------------------------------------------------------

What can I do to solve this problem?
Additionally, as I know, the MTTK pressure coupling method only supports
isotropic scaling.
But I want to use the MTTK method with semi-isotropic scaling because my
system is membrane system.
Is there any trick for using the MTTK method with semi-isotropic scaling?

Here is the input parameters that I used.
=============================
integrator                   = md-vv
dt                              = 0.002
nsteps                        = 500000
nstlog                        = 100
nstxout                       = 500
nstenergy                   = 500
nstlist                        = 10
rlist                           = 1.2
coulombtype               = pme
rcoulomb                    = 1.2
cutoff-scheme             = group
vdw-type                    = switch
rvdw_switch                = 1.0
rvdw                          = 1.2
tcoupl                        = nose-hoover
tc-grps                       = SYSTEM
tau-t                          = 0.1
nsttcouple                   = 1
ref-t                          = 323
pcoupl                        = MTTK
pcoupltype                  = isotropic
tau-p                         = 1.0
compressibility            = 4.5e-5 0.0
ref-p                         = 1.0
constraints                 = all-bonds
constraint_algorithm    = shake
=============================

Best,
Jumin


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