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+====== How to choose the NGRIDS in &MGRID ======
+The three inputs "CUTOFF", "NGRIDS", and "REL_CUTOFF" are important
+for accuracy and efficiency. The problem is that both, "accuracy and
+efficiency" depend on the combination of chosen values. See also the [[faq:cutoff|FAQ about cutoffs]].
+In an optimal setting you can proceed the following way:
+) choose a high enough value for REL_CUTOFF
+   this is system and basis set independent. It determines the
+   minimal cutoff used to bring a Gaussian function on the real space grid.
+   High values mean high accuracy, low values faster execution.
+) choose your cutoff and number of grids. This will determine the real space grids
+   for your calulcation, e.g. cutoff=400 ngrids=4
+   grid1 = 400, grid2 = 200, grid3 =100, grid4 = 50 (not actual numbers)
+   The cutoff should be high enough to take on the Gaussian with the largest exponent,
+   i.e. exponent*REL_CUTOFF <= cutoff (where exponent is for a product Gaussian)
+   If you choose more grids the mapping (Gaussian->Grid) is better but you have more
+   overhead from more grids (mostly FFTs).