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14 General recommendations for the PSCTR files


If a very accurate pseudopotential has to be created it is savest and simplest to create 2 projectors for each l-quantum number and chose the truncated AE-potential as local potential. As cutoff radius use half the nearest neighbor distance, and a relatively small value for the cutoff of the local potential. For Hg we have used the following reference potential:

   LULTRA =        T    use ultrasoft PP ?
   RCLOC  =      2.0    use i.e 2/3 of the radial cutoff 

     l     E      TYP  RCUT    TYP  RCUT
     2   .000      7  2.800    23  2.900
     2  -.790      7  2.800    23  2.900
     0   .000     15  2.900    23  2.900
     0  -.400     15  2.900    23  2.900
     1   .000     15  2.900    23  2.900
     1  -.400     15  2.900    23  2.900
This PP is much better than for example a standard BHS pseudopotentials, and the convergence speed is also reasonable. To improve efficiency it is possible to increase the radial cutoffs for the US-part in our example up to 3.2 a.u., and that one of the normconserving part to 3.0 a.u., without loss of accuracy.

Second, it is not always necessary to include two projectors per l-quantum number, for instance there is no need to make the s and p-part ultrasoft for the transition metals, and first row elements do not require an accurate description of the d-electrons. Examples are given below.

Mon Mar 29 10:38:29 MEST 1999