[ESPResSo] viscosity

[Guillaume Larsen]

dear all,

Let me first give a short description of my system:
particles + polymers in a 10*10*10 fully periodic box (setmd periodic 1 1 1).
interactions are LJ + FENE + Coulomb P3M.
An external force is applied to all particles and monomers along axis x.
The DPD thermostat is employed.
2 'plane cell' constraints are set up (min z axis and max z axis) + associated constraints (tunable slip+LJ)
The system is decomposed without verlet lists ('domain_decomposition -no_verlet_list').
I run the simulations using only one node since I plan to use the non-equilibrium MD calculation of the viscosity.
The system is decomposed into to 2 slabs for NEMD.

My questions are:
-how come the viscosity returned by the function 'nemd viscosity' can have negative values?
-When i run the simulation with few particles (100 particles + 20*10 monomers), ESPResSo returns something. But I want to add more particles (like 600+400) here is another problem : with a shield equals to 0.8 for instance, ESPResSo can not create the polymers (not enough space?) and with a lower value of the shield (0.2) the following errors occur : {086 particle coordinate out of range ...} and {063 plane constraint 0 violated by particle...}. It seems that polymers can not be created due to the different interactions...

Thank you in advance for your help and suggestions!

Guillaume

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