[gmx-users] Fatal error: Invalid T coupling input: 0 groups, 1 ref-t values and 1 tau-t values

[Gonzalez Fernandez, Cristina]

Dear Gromacs users,

I am trying to perform a NVT equilibration. However, I obtain this error:

Fatal error:
Invalid T coupling input: 0 groups, 1 ref-t values and 1 tau-t values

I don't understand the problem because I don't have defined any group,  I am indicating the ref-t and tau-t for the whole system.

My .mdp file is:

define          = -DPOSRES      ; position restrain the lipid

; Run parameters
integrator      = md            ; leap-frog integrator
nsteps          = 50000         ; 2 * 50000 = 100 ps
dt                 = 0.002             ; 2 fs

; Output control
nstxout         = 500           ; save coordinates every 1.0 ps
nstvout         = 500           ; save velocities every 1.0 ps
nstenergy       = 500           ; save energies every 1.0 ps
nstlog          = 500           ; update log file every 1.0 ps

; Bond parameters
continuation            = no            ; first dynamics run
constraint_algorithm    = lincs     ; holonomic constraints
constraints                 = all-bonds ; all bonds (even heavy atom-H bonds) constrained
lincs_iter                  = 1             ; accuracy of LINCS
lincs_order                 = 4             ; also related to accuracy

; Neighborsearching
cutoff-scheme   = Verlet
ns_type             = grid              ; search neighboring grid cells
nstlist             = 10                ; 20 fs, largely irrelevant with Verlet
rcoulomb            = 1.2               ; short-range electrostatic cutoff (in nm)
rvdw                = 1.2               ; short-range van der Waals cutoff (in nm)

; Electrostatics
coulombtype         = PME       ; Particle Mesh Ewald for long-range electrostatics
pme_order           = 4         ; cubic interpolation
fourierspacing  = 0.16  ; grid spacing for FFT

; Temperature coupling is on
tcoupl          = nose-hoover          ; nose-hoover thermostat
tau_t           = 0.1                ; time constant, in ps
ref_t           = 298                ; reference temperature, one for each group, in K

; Pressure coupling is off
pcoupl          = no            ; no pressure coupling in NVT

; Periodic boundary conditions
pbc             = xyz               ; 3-D PBC

; Dispersion correction
DispCorr        = EnerPres      ; account for cut-off vdW scheme

; Velocity generation
gen_vel         = yes           ; assign velocities from Maxwell distribution
gen_temp        = 298           ; temperature for Maxwell distribution
gen_seed        = -1            ; generate a random seed


Could anyone help me?

Thank you in advance,
C.