[gmx-users] vaccum simulation error

[Rajalakshmi.C]

hi all,
i am trying to simulate polymer chains in solvent and vacuum media using 45a3
forcefield. for vacuum simulation i used different md parameters than that of
solvent media. first i put 100ps NVT and then 100ps NPT. i sucessfully got NVT
done but for NPT i got following error ,

WARNING 1 [file npt-pr.mdp, line unknown]:
  Turning off pressure coupling for vacuum system


NOTE 1 [file npt-pr.mdp, line unknown]:
  Tumbling and or flying ice-cubes: We are not removing rotation around
  center of mass in a non-periodic system. You should probably set
  comm_mode = ANGULAR.

Too many warnings (1), grompp_mpicc terminated.
If you are sure all warnings are harmless, use the -maxwarn option.

the parameters for NPT are;
nstlist                  = 10
ns-type                  = simple
pbc                      = no
rlist                    = 0
coulombtype              = cut-off
rcoulomb                 = 0
fourierspacing		 = 0.12
vdw-type                 = cut-off
pme_order                = 4
rvdw                     = 0
ewald_rtol               = 0.00001
Tcoupl                   = v-rescale
tc-grps                  = PMH	
tau_t                    = 0.1      	
ref_t                    = 300    
Pcoupl                   = Berendsen
Pcoupltype               = Isotropic
tau_p                    = 0.5
compressibility          = 4.5e-5
ref_p                    = 1.0
DispCorr                 = no

can anyone suggest the solution for this vacuum simulation  
thanks in advance


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