[gmx-users] Enthalpy calculation in NPT ensemble

[Pelin S Bulutoglu]

Dear GROMACS users,

I am working on simulating a glycine crystal using GAFF force field with CNDO point charges in an NPT ensemble. I want to calculate the enthalpy and Cp of the crystal. However, the list that comes up following gmx energy command does not include the enthalpy or PV options, as it would normally do for NPT simulations. Does this mean that the simulation does not exhibit NPT behavior? I believe that this is not the case, since upon inspection of the temperature and pressure values, I found that they are both constant (within statistical error) throughout the simulation. What may be the cause of this? The following are some of my input parameters:

   cutoff-scheme                  = Verlet
   nstlist                        = 40
   ns-type                        = Grid
   pbc                            = xyz
   verlet-buffer-tolerance        = 0.005
   rlist                          = 1.4
   coulombtype                    = PME
   coulomb-modifier               = Potential-shift
   rcoulomb-switch                = 0
   rcoulomb                       = 1.4
   rvdw                           = 1.4
   DispCorr                       = EnerPres
   table-extension                = 1
   fourierspacing                 = 0.12
   pme-order                      = 4
   tcoupl                         = V-rescale
   nsttcouple                     = 10
   pcoupl                         = Berendsen
   pcoupltype                     = Anisotropic
   nstpcouple                     = 10
   tau-p                          = 2
   compressibility (3x3):
      compressibility[    0]={ 4.50000e-05,  4.50000e-05,  4.50000e-05}
      compressibility[    1]={ 4.50000e-05,  4.50000e-05,  4.50000e-05}
      compressibility[    2]={ 4.50000e-05,  4.50000e-05,  4.50000e-05}
   ref-p (3x3):
      ref-p[    0]={ 1.00000e+00,  1.00000e+00,  1.00000e+00}
      ref-p[    1]={ 1.00000e+00,  1.00000e+00,  1.00000e+00}
      ref-p[    2]={ 1.00000e+00,  1.00000e+00,  1.00000e+00}
   refcoord-scaling               = COM

Any input would be greatly appreciated. Thanks in advance.

Pelin Su Bulutoglu