Setting Electronic Temperature in Fermi-Dirac smearing

[Kendric Roberts]

Hi I am new to cp2k and am wondering when using smearing for cell/geometry optimization how should one choose a temperature, which gives very good scf convergence, but will give inaccurate results? Thanks for the help. 

-Kendric Roberts

[Lucas Lodeiro]

Hi Kendric, the smearing is a contraption to can converge a SCF calculation when the HOMO and LUMO are very near in energy (or the band gap is zero), that is the case for metals or semimetals (because in the SCF procedure you can get some metalic states in the middle of SCF or in some step of your DM). The smearing contribute with entropic-termic energy, and that is a problem, it can fix the SCF but gives some problem in energy, for that is ideal to use a little value for it, but it cannot be too little neither, because a too little value is laki that does not use the smearing. the best way to get the better temperature is search (scan) from what value the energy is converged (by some criteria ej 10E-4 Ha/atom), and then you can know too what is the minimum value to does not have problems in the SCF calculation, you can use one or some configurations. I use in metalics and semimetalics surfaces a value among 0.01 to 0.001 Ha (it is the kb*T energy of smearing, it is around 1000 to 100 K)

i hope i help you

regards

2018-07-31 13:14 GMT-04:00 Kendric Roberts <robertsk...@gmail.com>:

Hi I am new to cp2k and am wondering when using smearing for cell/geometry optimization how should one choose a temperature, which gives very good scf convergence, but will give inaccurate results? Thanks for the help. 

-Kendric Roberts

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[Kendric Roberts]

Okay, thank you very much for the help, I really appreciate. 

On Tuesday, July 31, 2018 at 8:37:59 PM UTC-7, Lucas Lodeiro wrote:

Hi Kendric, the smearing is a contraption to can converge a SCF calculation when the HOMO and LUMO are very near in energy (or the band gap is zero), that is the case for metals or semimetals (because in the SCF procedure you can get some metalic states in the middle of SCF or in some step of your DM). The smearing contribute with entropic-termic energy, and that is a problem, it can fix the SCF but gives some problem in energy, for that is ideal to use a little value for it, but it cannot be too little neither, because a too little value is laki that does not use the smearing. the best way to get the better temperature is search (scan) from what value the energy is converged (by some criteria ej 10E-4 Ha/atom), and then you can know too what is the minimum value to does not have problems in the SCF calculation, you can use one or some configurations. I use in metalics and semimetalics surfaces a value among 0.01 to 0.001 Ha (it is the kb*T energy of smearing, it is around 1000 to 100 K)

i hope i help you

regards

2018-07-31 13:14 GMT-04:00 Kendric Roberts <robertsk...@gmail.com>:

Hi I am new to cp2k and am wondering when using smearing for cell/geometry optimization how should one choose a temperature, which gives very good scf convergence, but will give inaccurate results? Thanks for the help. 

-Kendric Roberts

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