ENERGY DRIFT

[Daqiang]

Hi Dr Dubbeldam:
   I used the RASPA2.0.3 to simulate the isotherm of acetylene. However, when the pressure is higher than about 1500 Pa, I got a warning in the output file.
   
Simulation finished,  1 warnings
WARNING: ENERGY DRIFT (INTERNAL CONSISTENCY ERROR IN THE CODE), THE SIMULATION RESULTS ARE WRONG!!

How can I resolve the warning? Adding the NumberOfCycles?

Thanks,

Daqiang

[David Dubbeldam]

For any error, always retry with the latest version (which is RASPA 2.0.30).

[Daqiang]

Thank David. Using the latest version, I have resolve the issue.

[Somananda Sanyal]

Dear Dr. Dubbeldam,

    I am getting the same error with the latest version of RASPA, i.e. 2.0.35.
How to resolve the warning and if I may know too why is it occurring?

Thanks.
Somananda

[David Dubbeldam]

This can possibly occur when not all potentials are well-defined. An example is when the hydrogens do NOT have a Lennard-Jones potential, but the connecting atom has a VDW radius that encompasses the hydrogen (or it should). But if the VDW radius is too small, then at high density the atoms will start to overlap leading to numerical problems.

[kokojiang]

Dear Dr. Dubbeldam,

    I am getting the same error too. Like what you explained, the error happened as the number of adsorbates increased. When the number of adsorbates is low, it works well. But when the number of adsorbates is large, like 2500, the error appeared. In the forcefield I use, hydrogens did have no lennard-jones potential. How can I solve this warning? Should I change the forcefield or just run a larger simulation cycle?

Thank you!.
Jiang

[David Dubbeldam]

I would modify the force field. One of the options is to put a hard-sphere potential around the hydrogen to shield it from overlap.

[neumannrf]

Dear Dr. Dubbeldam,

We are having a similar problem with C2H2 and would like to try your suggestion, but we could not find in the manual how to set up a hard-sphere potential on the Hydrogen. What are the keyword and parameters?

[Martin li]

I'm having the same problem. How do I set the hard sphere potential?

[cmoralesd]

I'm having the same problem. How do I set the hard sphere potential?

In the force_field_mixinxing_rules.def you define your hard sphere potential for the desired atom type. Here a minimal example

Code Select Expand

# general rule for shifted vs truncated
truncated
# general rule tailcorrections
yes
# number of defined interactions
1
# type,        interaction,                   sigma [A]
H_CH           hard-sphere                    1.000