Hi GMX Users, We are computing the chemical potential of different gas molecules in a polymer melt with the tpi integrator. The computations are done for CO2 and CH4. The previous computations were done with v4.5.5 or 4.5.7 and gave equal results.
I recently switched to gromacs version 4.6.1, and the chemical potential computed by this version is shifted by a nearly constant factor, which is different for the two gas molecules. We are perplexed what causes this shift. Was there any change in the new version that affects the tpi integration? I will provide the mdp file we used below. The tpi integration is run on basis of the last 10 ns of a 30 ns NVT simulation with 'mdrun -rerun'. Best regards, Niels. ######################### The mdp file: ######################### ; VARIOUS PREPROCESSING OPTIONS cpp = cpp include = define = ; RUN CONTROL PARAMETERS integrator = tpi ; Start time and timestep in ps tinit = 0 dt = 0.001 nsteps = 1000000 ; For exact run continuation or redoing part of a run init_step = 0 ; mode for center of mass motion removal comm-mode = Linear ; number of steps for center of mass motion removal nstcomm = 1 ; group(s) for center of mass motion removal comm-grps = ; LANGEVIN DYNAMICS OPTIONS ; Temperature, friction coefficient (amu/ps) and random seed bd-fric = 0.5 ld-seed = 1993 ; ENERGY MINIMIZATION OPTIONS ; Force tolerance and initial step-size emtol = 100 emstep = 0.01 ; Max number of iterations in relax_shells niter = 20 ; Step size (1/ps^2) for minimization of flexible constraints fcstep = 0 ; Frequency of steepest descents steps when doing CG nstcgsteep = 1000 nbfgscorr = 10 ; OUTPUT CONTROL OPTIONS ; Output frequency for coords (x), velocities (v) and forces (f) nstxout = 100 nstvout = 0 nstfout = 0 ; Checkpointing helps you continue after crashes nstcheckpoint = 100 ; Output frequency for energies to log file and energy file nstlog = 100 nstenergy = 100 ; Output frequency and precision for xtc file nstxtcout = 0 xtc-precision = 1000 ; This selects the subset of atoms for the xtc file. You can ; select multiple groups. By default all atoms will be written. xtc-grps = ; Selection of energy groups energygrps = ; NEIGHBORSEARCHING PARAMETERS ; nblist update frequency nstlist = 5 ; ns algorithm (simple or grid) ns_type = grid ; Periodic boundary conditions: xyz (default), no (vacuum) ; or full (infinite systems only) pbc = xyz ; nblist cut-off rlist = 0.9 domain-decomposition = no ; OPTIONS FOR ELECTROSTATICS AND VDW ; Method for doing electrostatics coulombtype = pme rcoulomb-switch = 0 rcoulomb = 0.9 ; Dielectric constant (DC) for cut-off or DC of reaction field epsilon-r = 1 ; Method for doing Van der Waals vdw-type = Cut-off ; cut-off lengths rvdw-switch = 0 rvdw = 0.9 ; Apply long range dispersion corrections for Energy and Pressure DispCorr = EnerPres ; Extension of the potential lookup tables beyond the cut-off table-extension = 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 = 4 ewald_rtol = 1e-05 ewald_geometry = 3d epsilon_surface = 0 optimize_fft = no ; GENERALIZED BORN ELECTROSTATICS ; Algorithm for calculating Born radii gb_algorithm = Still ; Frequency of calculating the Born radii inside rlist nstgbradii = 1 ; Cutoff for Born radii calculation; the contribution from atoms ; between rlist and rgbradii is updated every nstlist steps rgbradii = 2 ; Salt concentration in M for Generalized Born models gb_saltconc = 0 ; IMPLICIT SOLVENT (for use with Generalized Born electrostatics) implicit_solvent = No ; OPTIONS FOR WEAK COUPLING ALGORITHMS ; Temperature coupling Tcoupl = V-rescale ; Groups to couple separately tc-grps = System ; Time constant (ps) and reference temperature (K) tau_t = 0.1 ref_t = 318 ; Pressure coupling Pcoupl = Parrinello-Rahman Pcoupltype = isotropic ; Time constant (ps), compressibility (1/bar) and reference P (bar) tau_p = 5.0 compressibility = 4.5e-5 ref_p = 1.0 ; Random seed for Andersen thermostat andersen_seed = 815131 ; SIMULATED ANNEALING ; Type of annealing for each temperature group (no/single/periodic) annealing = no ; Number of time points to use for specifying annealing in each group annealing_npoints = ; List of times at the annealing points for each group annealing_time = ; Temp. at each annealing point, for each group. annealing_temp = ; GENERATE VELOCITIES FOR STARTUP RUN gen_vel = yes gen_temp = 400 gen_seed = 1993 ; OPTIONS FOR BONDS ;constraints = none constraints = all-bonds ; Type of constraint algorithm constraint-algorithm = Lincs ; Do not constrain the start configuration unconstrained-start = no ; Use successive overrelaxation to reduce the number of shake iterations Shake-SOR = no ; Relative tolerance of shake shake-tol = 1e-04 ; Highest order in the expansion of the constraint coupling matrix lincs-order = 4 ; Number of iterations in the final step of LINCS. 1 is fine for ; normal simulations, but use 2 to conserve energy in NVE runs. ; For energy minimization with constraints it should be 4 to 8. lincs-iter = 1 ; Lincs will write a warning to the stderr if in one step a bond ; rotates over more degrees than lincs-warnangle = 30 ; Convert harmonic bonds to morse potentials morse = no ; ENERGY GROUP EXCLUSIONS ; Pairs of energy groups for which all non-bonded interactions are excluded energygrp_excl = ; NMR refinement stuff ; Distance restraints type: No, Simple or Ensemble disre = No ; Force weighting of pairs in one distance restraint: Conservative or Equal disre-weighting = Conservative ; Use sqrt of the time averaged times the instantaneous violation disre-mixed = no disre-fc = 1000 disre-tau = 0 ; Output frequency for pair distances to energy file nstdisreout = 100 ; Orientation restraints: No or Yes orire = no ; Orientation restraints force constant and tau for time averaging orire-fc = 0 orire-tau = 0 orire-fitgrp = ; Output frequency for trace(SD) to energy file nstorireout = 100 ; Dihedral angle restraints: No, Simple or Ensemble dihre = No dihre-fc = 1000 dihre-tau = 0 ; Output frequency for dihedral values to energy file nstdihreout = 100 ; Free energy control stuff free-energy = no init-lambda = 0 delta-lambda = 0 sc-alpha = 0 sc-sigma = 0.3 ; Non-equilibrium MD stuff acc-grps = accelerate = freezegrps = freezedim = cos-acceleration = 0 -- gmx-users mailing list gmx-users@gromacs.org http://lists.gromacs.org/mailman/listinfo/gmx-users * Please search the archive at http://www.gromacs.org/Support/Mailing_Lists/Search before posting! * Please don't post (un)subscribe requests to the list. Use the www interface or send it to gmx-users-requ...@gromacs.org. * Can't post? Read http://www.gromacs.org/Support/Mailing_Lists
