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["D. R. Hamann" <drh@bell-labs.com>]

Dear all,

I just discovered that the following from my last posting is inaccurate - in fact the old routine psp6cc.F90 is still being used.  I will test the new version, now activated by setting optnlxccc = 2, and report back.  The 4th derivative of the FHI core model in question appears to be discontinuous at the matching point but not singular, so there may well be an improvement.  I'll report back.

Don Hamann

The issue is not the presence or absence of a core charge.  I deliberately chose the *.pspnc's because they do have core charges.  However, unlike the FHI psp's, these use an analytic function for the core models and the Abinit routines that process these for the rest of the code do everything analytically.  The numerical FHI charges are processed by psp6cc.f in 4.2.4.  I found that even with an analytic charge input as a numerical table, this routine treated derivatives inconsistently and produced systematic errors.  In more recent version (4.4+ and maybe 4.3) my revised routine psp6cc_drh.F90 is the default, which leads to accurate comparisons between numerical and analytic derivatives for sufficiently smooth model charges.  A problem can still arise, however, for "spliced" functions because up to 4th derivatives are used in spline interpolations.  These problems are undoubtedly worse for GGA.

I

-- 
D. R. Hamann				Phone: 908-582-4454
Director, Theoretical Materials    	Fax:   908-582-4702
  Physics Research (retired)		email: drh@physics.bell-labs.com
Bell Laboratories 
Lucent Technologies
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