# Fatal error: Requested Parrinello-Rahman barostat with md-vv

**URL:** <https://gromacs.bioexcel.eu/t/fatal-error-requested-parrinello-rahman-barostat-with-md-vv/4739>\
**Category:** User discussions\
**Tags:** mdp-parameters, mdrun\
**Created:** [September 5, 2022, 9:29am UTC](https://gromacs.bioexcel.eu/t/fatal-error-requested-parrinello-rahman-barostat-with-md-vv/4739 "2022-09-05T09:29:52Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Veronika\_Vrankova](https://avatars.discourse-cdn.com/v4/letter/v/dbc845/32.png) [@Veronika\_Vrankova](https://gromacs.bioexcel.eu/u/Veronika_Vrankova)\
**Post date:** [September 5, 2022, 9:29am UTC](https://gromacs.bioexcel.eu/t/fatal-error-requested-parrinello-rahman-barostat-with-md-vv/4739/1 "2022-09-05T09:29:52Z")

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GROMACS version: 2021.3gpu  
GROMACS modification: No  
Hi everyone, I am trying to set up the simulation of protein dimer in solvent using **md-vv** integrator, **Nosé-Hoover chains** termostat and **Parinello-Rahman** barostat. I get following **Fatal error:**

**Requested Parrinello-Rahman barostat with md-vv. This combination is only  
available in the modular simulator. Some other selected options are, however,  
only available in the legacy simulator. Use a different pressure control  
algorithm.**

I get that some mdp options are causing this, but I have no idea which ones. Here is my input mdp file:

; Run parameters

integrator = md-vv ; velocity verlet

nsteps = 50000000 ; 2 \* 50000000 = 100000 ps (100 ns)  
dt = 0.002 ; 2 fs

; Output control

nstxout = 50000 ; suppress bulky .trr file by specifying  
nstvout = 50000 ; 0 for output frequency of nstxout,  
nstfout = 50000 ; nstvout, and nstfout  
nstenergy = 5000 ; save energies every 10.0 ps  
nstlog = 50000 ; update log file every 100.0 ps  
nstxout-compressed = 5000 ; save compressed coordinates every 10.0 ps  
compressed-x-grps = System ; save the whole system

; Bond parameters

continuation = yes ; Restarting after NPT  
constraint\_algorithm = lincs ; holonomic constraints  
constraints = h-bonds ; bonds involving H are constrained  
lincs\_iter = 1 ; accuracy of LINCS  
lincs\_order = 4 ; also related to accuracy

; Neighborsearching

cutoff-scheme = Verlet ; Buffered neighbor searching  
ns\_type = grid ; search neighboring grid cells  
nstlist = 10 ; 20 fs, largely irrelevant with Verlet scheme  
rlist = 1.2

; Electrostatics

coulombtype = PME ; Particle Mesh Ewald for long-range electrostatics  
rcoulomb = 1.2 ; short-range electrostatic cutoff (in nm)  
pme\_order = 4 ; cubic interpolation  
fourierspacing = 0.12 ; grid spacing for FFT  
vdwtype = cutoff  
vdw-modifier = force-switch  
rvdw = 1.2 ; short-range van der Waals cutoff (in nm)  
rvdw-switch = 1.0

; Temperature coupling is on

tcoupl = nose-hoover  
nsttcouple = 1  
nh-chain-length = 10  
tc-grps = Protein Non-Protein ; two coupling groups - more accurate  
tau\_t = 0.5 0.5 ; time constant, in ps  
ref\_t = 300 300 ; reference temperature, one for each group, in K

; Pressure coupling is on

pcoupl = Parrinello-Rahman ; Pressure coupling on in NPT  
pcoupltype = isotropic ; uniform scaling of box vectors  
tau\_p = 2.0 ; time constant, in ps  
ref\_p = 1.0 ; reference pressure, in bar  
compressibility = 4.5e-5 ; isothermal compressibility of water, bar^-1

; Periodic boundary conditions

pbc = xyz ; 3-D PBC

; Dispersion correction

DispCorr = no ; account for cut-off vdW scheme

; Velocity generation

gen\_vel = no ; Velocity generation is off

**I will be very grateful for your help to overcome this issue.**

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<div class="post-metadata">

**Author:** ![alevilla](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/alevilla/32/439_2.png) [@alevilla](https://gromacs.bioexcel.eu/u/alevilla)\
**Post date:** [September 6, 2022, 8:22am UTC](https://gromacs.bioexcel.eu/t/fatal-error-requested-parrinello-rahman-barostat-with-md-vv/4739/2 "2022-09-06T08:22:40Z")

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Hi,  
the error suggests to change the pressure control algorithm, that is defined by the `pcoupl =` option in mdp file.  
You can use Martyna-Tuckerman-Tobias-Klein implementation in place of Parrinello-Rahman.

See here more on velocity-verlet integrator [Molecular Dynamics — GROMACS 2022.3 documentation](https://manual.gromacs.org/current/reference-manual/algorithms/molecular-dynamics.html#the-velocity-verlet-integrator)

here on barostat implementation [Molecular Dynamics — GROMACS 2022.3 documentation](https://manual.gromacs.org/current/reference-manual/algorithms/molecular-dynamics.html#mttk-pressure-control-algorithms)

here on mdp option [Molecular dynamics parameters (.mdp options) — GROMACS 2022.3 documentation](https://manual.gromacs.org/current/user-guide/mdp-options.html)

I hope it helps  
\Alessandra