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exercises:2018_uol_school:converging_cutoff [2018/05/31 10:10] – [Analysis] mwatkinsexercises:2018_uol_school:converging_cutoff [2018/05/31 14:44] – [Input files] mwatkins
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 This exercise is similar to the previous one, but uses a setup and system more typical of CP2K usage. We will use a system of 32 H<sub>2</sub>O water molecules within a periodic box. Here is the input template: This exercise is similar to the previous one, but uses a setup and system more typical of CP2K usage. We will use a system of 32 H<sub>2</sub>O water molecules within a periodic box. Here is the input template:
  
-<code>+<code cp2k input_template.inp>
 &GLOBAL &GLOBAL
   PRINT_LEVEL MEDIUM   PRINT_LEVEL MEDIUM
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 Compared to the Si example, this is a larger system, we are using the OT optimizer in a good setup for a small to medium insulating system: Compared to the Si example, this is a larger system, we are using the OT optimizer in a good setup for a small to medium insulating system:
  
-<code>+<code cp2k>
     &SCF     &SCF
       SCF_GUESS RESTART       SCF_GUESS RESTART
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 and we are also saving the forces on the atoms and we are also saving the forces on the atoms
  
-<code>+<code cp2k>
   &PRINT   &PRINT
     &FORCES     &FORCES
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 we see that the largest exponent is only 2.7 Bohr<sup>-2</sup>, so can be represented on a much coarser grid. we see that the largest exponent is only 2.7 Bohr<sup>-2</sup>, so can be represented on a much coarser grid.
  
-<note>Task +<note>**Task** 
-If you like, have a look at the BASIS_MOLOPT file (in the data directory, or online [[https://sourceforge.net/p/cp2k/code/HEAD/tree/trunk/cp2k/data/BASIS_MOLOPT|here]]) and see how the exponents change across the periodic table.+If you like, have a look at the BASIS_MOLOPT file (in the data directory, or online [[https://sourceforge.net/p/cp2k/code/HEAD/tree/trunk/cp2k/data/BASIS_MOLOPT|here]]) and see how the exponents change across the periodic table
 </note> </note>
 +
 +The convergence is largely dominated by the calculation of the gradient terms in a GGA functional (compare a simulation with LDA to the PBE used here). The evaluation of these terms on the grids are demanding, and very dependent on the functional.
 +
 +<code>
 +    &XC
 +      &XC_FUNCTIONAL PBE
 +      &END XC_FUNCTIONAL
 +      &XC_GRID
 +        ! defaults
 +        XC_SMOOTH_RHO NONE
 +        XC_DERIV PW
 +      &END XC_GRID
 +    &END XC
 +</code>
 +
 +For BLYP functional some smoothing needs to be applied. The smoothing may also converge forces more rapidly than the default settings, but at the expense of modifying the functional slightly.
 +
 +<note>**TASKS**
 +
 +compare to the previous calculation, but using a smoothing section in the XC section.
 +
 +<code>
 +    &XC
 +      &XC_FUNCTIONAL PBE
 +      &END XC_FUNCTIONAL
 +      &XC_GRID
 +        XC_SMOOTH_RHO NN50
 +        XC_DERIV NN50_SMOOTH
 +      &END
 +    &END XC
 +</code>
 +  
 +compare the convergence of LDA and BLYP to PBE.
 +
 +<code>
 +&XC_FUNCTIONAL PADE # or BLYP
 +&END XC_FUNCTIONAL
 +</code>
 +</note>
 +
 +<note tip>
 +Also change the psuedo potential to the appropriate functional.
 +<code>
 +    &KIND O
 +      BASIS_SET DZVP-MOLOPT-SR-GTH-q6
 +      POTENTIAL GTH-PADE-q6
 +    &END KIND
 +</code>
 +PADE is a synonym for LDA.
 +</note>
 +
events/2018_summer_school/converging_cutoff.txt · Last modified: 2020/08/21 10:15 by 127.0.0.1