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--- exercises:2018_uol_school:converging_cutoff [2018/05/31 10:10] – [Analysis] mwatkins
+++ exercises:2018_uol_school:converging_cutoff [2018/05/31 13:08] – [Analysis] mwatkins
@@ Line 193: / Line 193: @@
 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>
+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>