events:2018_summer_school:converging_cutoff
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exercises:2018_uol_school:converging_cutoff [2018/05/31 10:08] – [Analysis] mwatkins | events:2018_summer_school:converging_cutoff [2018/06/11 09:54] – ↷ Page moved from exercises:2018_uol_school:converging_cutoff to events:2018_summer_school:converging_cutoff ibethune | ||
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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< | 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< | ||
- | < | + | < |
&GLOBAL | &GLOBAL | ||
PRINT_LEVEL MEDIUM | PRINT_LEVEL MEDIUM | ||
Line 91: | Line 91: | ||
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: | ||
- | < | + | < |
&SCF | &SCF | ||
SCF_GUESS RESTART | SCF_GUESS RESTART | ||
Line 109: | Line 109: | ||
and we are also saving the forces on the atoms | and we are also saving the forces on the atoms | ||
- | < | + | < |
&FORCES | &FORCES | ||
Line 192: | Line 192: | ||
we see that the largest exponent is only 2.7 Bohr< | we see that the largest exponent is only 2.7 Bohr< | ||
+ | |||
+ | < | ||
+ | If you like, have a look at the BASIS_MOLOPT file (in the data directory, or online [[https:// | ||
+ | </ | ||
+ | |||
+ | 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. | ||
+ | |||
+ | < | ||
+ | &XC | ||
+ | & | ||
+ | &END XC_FUNCTIONAL | ||
+ | & | ||
+ | ! defaults | ||
+ | XC_SMOOTH_RHO NONE | ||
+ | XC_DERIV PW | ||
+ | &END XC_GRID | ||
+ | &END XC | ||
+ | </ | ||
+ | |||
+ | 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. | ||
+ | |||
+ | < | ||
+ | |||
+ | compare to the previous calculation, | ||
+ | |||
+ | < | ||
+ | &XC | ||
+ | & | ||
+ | &END XC_FUNCTIONAL | ||
+ | & | ||
+ | XC_SMOOTH_RHO NN50 | ||
+ | XC_DERIV NN50_SMOOTH | ||
+ | &END | ||
+ | &END XC | ||
+ | </ | ||
+ | | ||
+ | compare the convergence of LDA and BLYP to PBE. | ||
+ | |||
+ | < | ||
+ | & | ||
+ | &END XC_FUNCTIONAL | ||
+ | </ | ||
+ | </ | ||
+ | |||
+ | <note tip> | ||
+ | Also change the psuedo potential to the appropriate functional. | ||
+ | < | ||
+ | &KIND O | ||
+ | BASIS_SET DZVP-MOLOPT-SR-GTH-q6 | ||
+ | POTENTIAL GTH-PADE-q6 | ||
+ | &END KIND | ||
+ | </ | ||
+ | PADE is a synonym for LDA. | ||
+ | </ | ||
+ |
events/2018_summer_school/converging_cutoff.txt · Last modified: 2020/08/21 10:15 by 127.0.0.1