[gmx-users] anisotropic pressure coupling

[Shuangxing Dai]

Hi all:
    I was using Parrinello-Rahman for pressure coupling and here is the mdp
file:

; RUN CONTROL PARAMETERS =
integrator               = sd
; start time and timestep in ps =
tinit                    = 0
dt                       = 0.001
nsteps                   = 200000
; number of steps for center of mass motion removal =
nstcomm                  = 100
; NEIGHBORSEARCHING PARAMETERS =
; nblist update frequency =
nstlist                  = 50
; ns algorithm (simple or grid) =
ns_type                  = grid

;OPTIONS FOR PRESSURE COUPLING
Pcoupl                   = Parrinello-Rahman
pcoupltype               = anisotropic
tau_p                    = 1
compressibility          = 2.1645e-09  2.1645e-09 2.7322e-09 0 0 0
ref_p                    = 1 1 1 0 0 0
;OPTIONS FOR TEMPERATURE COUPLING
tc_grps                  = system
tau_t                    = 0.1
ref_t                    = 300
; OPTIONS FOR BONDS     =
constraints              = hbonds
; Type of constraint algorithm =
constraint-algorithm     = Lincs
; Do not constrain the start configuration =
unconstrained-start      = no
; Relative tolerance of shake =
shake-tol                = 0.0001
; Highest order in the expansion of the constraint coupling matrix =
lincs-order              = 12
; Lincs will write a warning to the stderr if in one step a bond =
; rotates over more degrees than =
lincs-warnangle          = 30
; Periodic boundary conditions: xyz, no, xy
pbc                      = xyz
periodic_molecules       = no
; nblist cut-off
rlist                    = 1

; OPTIONS FOR ELECTROSTATICS AND VDW
; Method for doing electrostatics
coulombtype              = PME
rcoulomb                 = 1
; Method for doing Van der Waals
vdw-type                 = Cut-off
; cut-off lengths
rvdw                     = 1

; Spacing for the PME/PPPM FFT grid
fourierspacing           = 0.12
; FFT grid size, when a value is 0 fourierspacing will be used
fourier_nx               = 0
fourier_ny               = 0
fourier_nz               = 0
; EWALD/PME/PPPM parameters
pme_order                = 6
ewald_rtol               = 1e-4
ewald_geometry           = 3d
epsilon_surface          = 0
optimize_fft             = no

 It seems that the temperature coupling is fast and fluctuation is less that
1%. But the pressure coupling fails. The pressure fluctuates from +1e3 bar
to -1e3 bar. Anyone can help?


Thanks,
Shuangxing Dai
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