Hello,

I was trying to run the example to calculate the polaron from the recent example section. However while trying to run the second epw code for calculating the polaron, I ran into a problem. The crash file reads

task # 68

from polaron_prepare : error # 1

Illegal nhblock_plrn, should between 1 and nkf * nbnd_plrn

While I have not changed any lines from the given code, the only difference is the number of nodes used for the calculation. I dont know if that would create the problem.

Thanks in advance for the suggestion.

Pravin

## Problem with calculating polaron equation

**Moderator:** hlee

### Re: Problem with calculating polaron equation

Dear Pravin,

This problem occurs when you have more number of cores than k-points. As you said you have changed the number of nodes, how many nodes/cores you are using? Try to reduce the number of k-points and check if that works.

Otherwise, attach your input files.

Best,

Sabya.

This problem occurs when you have more number of cores than k-points. As you said you have changed the number of nodes, how many nodes/cores you are using? Try to reduce the number of k-points and check if that works.

Otherwise, attach your input files.

Best,

Sabya.

### Re: Problem with calculating polaron equation

Hello Sabya,

Thank you for your response. Currently I am using 1 node with 36 cores and get the problem. I had initially tried with 2 nodes with 72 cores and got the same error file. I preempted the number of cores might be the problem. I think I need to increase the number of k-points as I am only using 6 6 6 k points unless you suggest otherwise.

Thanks

Pravin

Thank you for your response. Currently I am using 1 node with 36 cores and get the problem. I had initially tried with 2 nodes with 72 cores and got the same error file. I preempted the number of cores might be the problem. I think I need to increase the number of k-points as I am only using 6 6 6 k points unless you suggest otherwise.

Thanks

Pravin

### Re: Problem with calculating polaron equation

Dear Pravin,

I agree with Sabya, this error occurs when the number of MPI processes is larger than the number of k-points in the fine grid (where the matrix elements will be interpolated and the polaron equations solved).

In the school example (lif.epw2.in), nkf1=nkf2=nk3=4, so the fine grid contains 4x4x4=64 k-points and you can use 64 cores at most; anything above that will trigger this error. Try running with less processes or, alternatively, increase the number of points in the fine grid.

Best,

Jon Lafuente-Bartolome

I agree with Sabya, this error occurs when the number of MPI processes is larger than the number of k-points in the fine grid (where the matrix elements will be interpolated and the polaron equations solved).

In the school example (lif.epw2.in), nkf1=nkf2=nk3=4, so the fine grid contains 4x4x4=64 k-points and you can use 64 cores at most; anything above that will trigger this error. Try running with less processes or, alternatively, increase the number of points in the fine grid.

Best,

Jon Lafuente-Bartolome