How do you determine how many ADDED_MOS to use?

[Dev Rana]

How do you determine how many ADDED_MOS to use?

I'm currently obtaining a warning:

 *** WARNING in qs_mo_occupation.F:492 :: Fermi-Dirac smearing includes ***

 *** the first MO                                                       ***

 *** WARNING in qs_mo_occupation.F:503 :: Fermi-Dirac smearing includes ***

 *** the last MO => Add more MOs for proper smearing.                   ***

However, I don't know how to choose the right number of MOs for proper smearing.

Best Regards,

Devyesh Rana

[Marcella Iannuzzi]

Dear Devyesh Rana

The first warning message is telling you that also the lowest states are involved in the smearing. 

This should be avoided. 

Probably you have a system with a narrow span in MOS energies and a too large smearing temperature. 

The number of added MOS depends on the density of states around Fermi. 

You want to cover a few eV, but how many depends on the smearing temperature you give.

Best

Marcella

[Dev Rana]

Hi Marcella,

Thank you for your response. I found this helpful reference which helps you determine the correct smearing temperature. It's not a simple calculation, but it guides you on how to find the optimal temperature based on some regression testing. I'm 100% sure that if they were to also plot time for simulation to complete, we would see an optimal smearing temperature which speeds up calculations as well. Albeit, with a sacrifice in precision. But could be possible.

Anyhow, reference: http://theossrv1.epfl.ch/Main/ElectronicTemperature

Best Regards,

Devyesh Rana

[Lucas Lodeiro]

Hi Dev,

As Marcella said, the number of MOs added is system dependent, but for a typical smearing temperature (1000-2000 K) if you add  20% of total occupied orbitals, usually works fine. This is the standard in some codes like Quantum Espresso.

--
You received this message because you are subscribed to the Google Groups "cp2k" group.
To unsubscribe from this group and stop receiving emails from it, send an email to cp2k+uns...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/cp2k/db7e0332-2578-4d0e-999c-6853acd7271cn%40googlegroups.com.

[Dev Rana]

Thank you Lucas, for that simple explanation. I'll try this out.