Pressure coupling incorrect number of values (I need exactly 1)

User discussions
1

GROMACS version: 2019.4
GROMACS modification: Yes/No
Here post your question I am trying to use the pull code to pull a group along a vector. I have the following pull code

pull = yes
pull_ncoords = 1 ; only one reaction coordinate
pull_ngroups = 2 ; two groups defining one reaction coordinate
pull-pbc-ref-prev-step-com = yes
pull_group1_name = PROF
pull_group2_name = PROG
pull_group1_pbcatom = 7367
pull_group2_pbcatom = 12925
pull_coord1_vec = 0 0 1
pull_coord1_type = umbrella ; harmonic potential
pull_coord1_geometry = direction-periodic ; simple distance increase
pull_coord1_dim = N N Y
pull_coord1_groups = 1 2
pull_coord1_start = yes ; define initial COM distance > 0
pull_coord1_rate = 0.01 ; 0.01 nm per ps = 10 nm per ns
pull_coord1_k = 1000 ; kJ mol^-1 nm^-2

and I get the following error

Pressure coupling incorrect number of values (I need exactly 1)

my question is, where/how do I set the pressure coupling in the mdp file such that the error wont occur? earlier in the mdp file there is a line about Pcoupl =Parinello-Rahman (which is exactly one thing?) but there is nothing in the file about Pcoupling which is numeric - should there be? what syntax do I use to pop it in there? Has anybody found the pull code documentation easy to extract solutions to problems from???

2

Hi,

either your reference pressure given with ref-p or your compressibility has not exactly one value, checking your .mdp file should help.

For ref-p using 1 and for compressibility 4.5e-5 should be fine.

3

Helllo, thanks for taking the time to help me! I think the issue was that extra difits had snuck into the power term so it read 4.5e-505 which was interpreted as zero. Then I had to change from isotropic to semiisotropic and it seemed to work alright (although in fac t my pull group wasn’t ideal). thanks again.

Matt