Dear All,
Thanks to all of you for your comments and suggestions.
I have considered all of them and did some tests.
I did different tests and when using the same program and removing the rigid bonds ( i have a 2d system of spheres) the temperature is preserved.
Also, as Stefan suggested I switch form rigid bonds to harmonic bonds
{ dpd 1.5 0.0 1.122462048309373 WF 1 1.0 1.122462048309373 TWF 1 }
{0 HARMONIC 1000.0 1.0 1.3} {0 0 lj-gen 1.0 1.0 1.020408163265306 0.1011256571291992 0.0 50 49 134.5526623421209 134.5526623421209 0.0 }
And now the temperature is fluctuating around 1.6$$... I had to use a very high value of K to keep the particle's center distance around 1.0.
So, I have to think more carefully what Stefan said: "Thermalization of rotational degrees of freedom is entirely different in Langevin than what happens when combining rigid bodies with DPD (this so far probably nobody has done)."
I would appreciate any extra comments and suggestions.
Thanks a lot,
Salvador