[ESPResSo-users] Thermostat, Rigid bond & Rotation feature

[Muhammad Anwar]

Hello,
Dear Users & Developers,
I am using espresso-2.2.0b and working on simulation of polymer melt, 
first i simulated a system with Lennard Jones particle without any 
bonded potential at constant temperature (I put temp 1) using Langevin 
thermostat. I calculated the temperature which fluctuate around 1 (0.99 
- 1.02) and total pressure is in three digits around 130. Then i added 
rigid bond my temperature fluctuate from 0.94 to 0.98 and total pressure 
increases to 6 digits around 490000. Then i added cos square bond angle 
potential, my temperature fluctuate from 0.64 to 0.69 and pressure again 
in 6 digits. Then i added dihedral potential as well and again 
temperature  fluctuate from 0.64 to 0.69 and pressure in 6 digits. I 
kept epsilon, sigma and other parameters in Lennard Jones and number of 
particles same.

I want to ask what reason might be for smaller value of temperature when 
adding bonded potentials and why pressure increases to a big value when 
add rigid bonds, does it make sense?
Secondly, when i activate ROTATION feature along with rigid bond, i get 
the message , currently i can not activate bond constraint and rotation 
feature together.
I am sorry for long email and thanks for your patience.

Best Regards,
Muhammad Anwar