npt simulation involves fix rigid

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1

Hi, all

I am trying to run npt simulations on a system consist of rigid model water, and rigid model CO2. I noticed that the temperature and pressure calculated is not correct, i.e. even at step zero. For example, I use velocity create to set the initial velocity of the system to be 10K, however, what I get at step zero is 8K. Also, during the npt simulation, I see my temperature rise dramatically but the output movie which indicates the molecular dynamics during the simulation is very stable, i.e., the temperature rise by 700 K but the system is not melting or blowing up. And all the calculated value of the KE and PE at each time step seems reasonable too.

I have searched the mailing list and I thought my problem is that I didn’t specify my fix command before the velocity command is issued, since I am using rigid body models and there are degree of freedom removed. So I switch the order of my code and hoping to see a difference, yet to find out that the temperature and pressure is still not correct.

Thus I have to turn the lammps community for help. Any comments are welcome and appreciated.

Thank you very much.

P.S. I have also attached a copy of my input file (‘ch4.lmp’) in here for your information.

Thanks again,
Qianping

ch4.lmp (2.23 KB)

2

Sorry that I forgot to attached my output file.

Hi, all

I am trying to run npt simulations on a system consist of rigid model water, and rigid model CO2. I noticed that the temperature and pressure calculated is not correct, i.e. even at step zero. For example, I use velocity create to set the initial velocity of the system to be 10K, however, what I get at step zero is 8K. Also, during the npt simulation, I see my temperature rise dramatically but the output movie which indicates the molecular dynamics during the simulation is very stable, i.e., the temperature rise by 700 K but the system is not melting or blowing up. And all the calculated value of the KE and PE at each time step seems reasonable too.

I have searched the mailing list and I thought my problem is that I didn’t specify my fix command before the velocity command is issued, since I am using rigid body models and there are degree of freedom removed. So I switch the order of my code and hoping to see a difference, yet to find out that the temperature and pressure is still not correct.

Thus I have to turn the lammps community for help. Any comments are welcome and appreciated.

Thank you very much.

P.S. I have also attached a copy of my input file (‘ch4.lmp’) in here for your information.

Thanks again,
Qianping

ch4.lmp (2.23 KB)

log.lammps (5.29 KB)