User Tools

Site Tools


events:2018_summer_school:converging_cutoff

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revision Previous revision
Next revision
Previous revision
events:2018_summer_school:converging_cutoff [2018/05/31 10:06]
mwatkins [Analysis]
events:2018_summer_school:converging_cutoff [2018/06/11 09:54] (current)
ibethune ↷ Page moved from exercises:2018_uol_school:converging_cutoff to events:2018_summer_school:converging_cutoff
Line 7: Line 7:
 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
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:
  
-<​code>​+<​code ​cp2k>
     &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
  
-<​code>​+<​code ​cp2k>
   &PRINT   &PRINT
     &FORCES     &FORCES
Line 177: Line 177:
 </​code>​ </​code>​
  
-That there is a Gaussian with an exponent of 10.4 Bohr<​sup>​-2</​sup>​.+That there is a Gaussian with an exponent of 10.4 Bohr<​sup>​-2</​sup>​. ​If we compare to the basis set for Silicon 
 + 
 +<​code>​ 
 + Si DZVP-MOLOPT-GTH DZVP-MOLOPT-GTH-q4 
 + 1 
 + 2 0 2 6 2 2 1 
 +      2.693604434572 ​ 0.015333179500 -0.073325401200 -0.005800105400 ​ 0.023996406700 ​ 0.043919650100 
 +      1.359613855428 -0.283798205000 ​ 0.484815594600 -0.059172026000 ​ 0.055459199900 ​ 0.134639409600 
 +      0.513245176029 -0.228939692700 -0.276015880000 ​ 0.121487149900 -0.269559268100 ​ 0.517732111300 
 +      0.326563011394 ​ 0.728834000900 -0.228394679700 ​ 0.423382421100 -0.259506329000 ​ 0.282311245100 
 +      0.139986977410 ​ 0.446205299300 -0.018311553000 ​ 0.474592116300 ​ 0.310318217600 ​ 0.281350794600 
 +      0.068212286977 ​ 0.122025292800 ​ 0.365245476200 ​ 0.250129397700 ​ 0.647414251100 ​ 0.139066843800 
 +</​code>​ 
 + 
 +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** 
 +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>​ 
 + 
 +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.1527761166.txt.gz · Last modified: 2018/05/31 10:06 by mwatkins