[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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

From: Muhammad Anwar
Subject: Re: [ESPResSo-users] Thermostat, Rigid bond & Rotation feature
Date: Tue, 7 Jun 2011 09:41:17 +0200
User-agent: Thunderbird (X11/20101027)

Axel Arnold wrote:

On Wednesday 01 June 2011, Muhammad Anwar wrote:
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.

Since you don't provide your script, we can only guess. However, the pressure presumably goes up since some particles are constrained at distances with high interaction; you might want to check the pressure components to see which interaction that is. You might want to exclude intramolecular nonbonded interactions, since they are meaningless in case of rigid bonds.

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.

If the pressure is too high, probably also some interaction is quite large, which might make it impossible for the thermostat to keep the temperature. Check with a smaller time step, e.g.

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?

See above.

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.

As it says, you cannot use ROTATION with rigid bonds. The reason is that there is no constraints algorithm for rotationally non-invariant particles. If you find a good one, you can try to implement it and contribute to Espresso.


Thank very much for your good suggestions, now i want to remove intra molecular non bonded interactions. I am using Lennard Jones non bonded interaction, I want monomers of different chains will interact with each other with Lennard Jones interactions but monomers of same chains don't interact with each other (intra molecular). Before this i defined two types of particles for all chains (each chain has two different types of particles) and defined Lennard Jones interaction for them. Will i need to define different types of particle for each chains (like for 1st chain 0,1 types, for 2nd 2,3 and so on) to remove intra molecular interactions or is there any simple way? Because in this case i will need to define interaction hundreds of time as number of chains will increase.
Thank you very much.

Best Regards,
Muhammad Anwar

reply via email to

[Prev in Thread] Current Thread [Next in Thread]