[CP2K-user] [CP2K:11662] How to perfom zero temperature geometry optimization

[Mohammad Shakiba]

Dear Patrick,

Thank you so much for your nice and detailed answer. That helped a lot.

On Sunday, May 5, 2019 at 5:04:44 PM UTC+4:30, Patrick Gono wrote:
>
> Dear Mohammad,
>
> Do you want to perform a geometry optimization (GEO_OPT), or a cell 
> optimization in which the cell parameters are varied as well?
>
> Geometry optimization is by its very nature a zero Kelvin method - after 
> all, you are minimizing energy to find the ground state of the 
> computational cell geometry. 
>
> So is cell optimization by default, but you can choose the MD type, which 
> uses (finite temperature) molecular dynamics to compute the stress tensor. 
> The MD section with the appropriate temperature must be defined in order to 
> use this method. But I suspect this is not really what you are after.
>
> Define the &GEO_OPT section and set up a GEO_OPT calculation to find the 
> optimized structure. Alternatively, if you want to relax the cell 
> parameters, go for CELL_OPT. The sections are quite similar, in both cases 
> I recommend the BFGS algorithm unless tou encounter instabilities in the 
> optimization process. You can find the appropriate tutorials on the 
> official cp2k website, or via Google.
>
> Regarding the smearing: as you yourself mention your system has a gap, I 
> would opt for a different scf method. Instead of direct diagonalization 
> (with or without smearing) consider adopting an orbital transformation 
> method (defined in the & OT section). These provide improved performance, 
> although may not be as reliable as diagonalization in some cases. However, 
> the OT methods work well for virtually any system I study. 
>
> Regardless, you chose the fermi-dirac smearing method which takes one 
> parameter, a temperature. This is not the real temperature of the system, 
> it's only a parameter of the smearing method. Using 0 K basically means no 
> smearing (the FD distribution is a step function at zero temperature). 
> Consider commenting out the smearing section if you do not intend to use 
> smearing.
>
> Yours sincerely, 
> Patrick Gono
>
> On Sun, 5 May 2019, 08:20 Mohammad Shakiba, <msha... at gmail.com 
> <javascript:>> wrote:
>
>> Hello everyone,
>>
>> What is the way to set the temperature during geometry optimization? 
>> Also, in the manual for CELL_OPT it says "*This section sets the 
>> environment for the optimization of the simulation cell. Two possible 
>> schemes are available: (1) Zero temperature optimization; (2) Finite 
>> temperature optimization." *but there is no section for setting the 
>> temperature (My system is a semiconductor).
>>
>> I also used Fermi-Dirac smearing function with the following inputs but 
>> that gives me an error after one scf step *"KS energy is an abnormal 
>> value (NaN/Inf).".*
>>
>>
>>  SCF WAVEFUNCTION OPTIMIZATION
>>
>>   Step     Update method      Time    Convergence         Total energy    
>> Change
>>   
>> ------------------------------------------------------------------------------
>>      1 P_Mix/Diag. 0.40E+00   30.0     1.31109320      -882.6554194381 
>> -8.83E+02
>>
>>
>>  *******************************************************************************
>>  *   
>> ___                                                                       *
>>  *  /   
>> \                                                                      *
>>  * 
>> [ABORT]                                                                     
>> *
>>  *  \___/                KS energy is an abnormal value 
>> (NaN/Inf).             *
>>  *    
>> |                                                                        *
>>  *  
>> O/|                                                                        *
>>  * /| 
>> |                                                                        *
>>  * / \                                                     
>> qs_ks_methods.F:866 *
>>
>>  *******************************************************************************
>>
>>
>>
>> Can any one help me in this regard? Thanks in advance.
>>
>> The smearing input section which provides the electronic temperature:
>>
>> &SCF
>>       SCF_GUESS ATOMIC
>>       MAX_SCF 300
>>       EPS_SCF 1.0E-7
>>       ADDED_MOS 20
>>       &DIAGONALIZATION
>>          ALGORITHM STANDARD
>>          EPS_ADAPT 0.01
>>       &END DIAGONALIZATION
>>       &SMEAR ON
>>         METHOD FERMI_DIRAC
>>         ELECTRONIC_TEMPERATURE [K] 0
>>       &END
>> &END SCF
>>
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>
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