UT theoretical chemistry code forum

Hi,
I am simulating impurity diffusion in iron with EON. I am getting few low barrier events (barrier lower than 0.1 eV) during EON run (file no_max_rate is attached). Then, I have read about the max_rate implementation to avoid such low barrier events (file max_rate is attached). Still, I am countering these low barrier events. In this regard, I have the following queries:
1. How to implement max_rate in EON to avoid such low-barrier events?
2. Are their other ways to avoid such low barrier events?
Any help will be appreciated.

Regards,
Sanjay Manda
Ph.D. Student
MEMS Department
IIT Bombay
India.

If you can make the simulation results available to me, I can take a look.

Hi,
Thank you so much for your response. As mentioned earlier, we are encountering many low barrier events (barrier lower than 0.1 eV) corresponding to impurity diffusion in Fe which are undesirable for our simulations. The desirable diffusion processes (interstitial diffusion across the lattice) are much slower compared to faster relaxations being sampled by EON. Therefore, we tried simulations with both max_rate implementation and coarse-graining.

1. Max_rate implementation:
Initially, we ran simulations without specifying the max_rate and many low-barrier events were observed as per the dynamics.txt file. These results are available in the folder “no max_rate”.
Then, we capped the max_rate at the value of 3e10 s-1. If we understand correctly, any events with a barrier higher than the max_rate should not occur. However, low-barrier events were observed even after implementing max_rate. Does EON implement max_rate in a strict sense or is it used as a guiding factor in the simulations? The corresponding results are placed in the folder “max_rate”.

2. Coarse graining:
Further, we tried both coarse-graining methods mentioned in the EON documentation: MCAMC and ASKMC.

In MCAMC, we opted for the transition-counting method. Though we observed the formation of super basins and a decrease in the rate around the super basins, still the system is not able to come out of the super basins. These results are placed in the folder “MCAMC”.

In ASKMC, the akmc.log file displayed a message “raising the barrier between state x to state y”. However, we did not see any change in the barrier and rate in the dynamics.txt file. The simulation results are placed in the folder “ASKMC”.

Our simulation results can be accessed through the following link:

https://drive.google.com/drive/folders/ ... share_link

Based on the above-mentioned trials, we have the following questions:
1. Does max_rate work in EON and what are the parameters? Why is it not working for our simulations?
2. Is it feasible to use coarse-graining methods (as implemented in EON) effectively for a complex system (several impurity atoms in Fe matrix) when there is a large separation in process rates between desirable and quasi-equilibrium processes?

Thanks, and Best Regards,
Sanjay Manda
Ph.D. Student
MEMS Department
IIT Bombay
India