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RMAX, RDEP, QCUT, QGAM tags


maximum radius for non local projection operators 



maximum radius for depletion charges 



low qvalue for optimization 



high qvalue for optimization 

These tags control the real space optimization of the pseudopotentials [47],
and the extend of the non local projection operators.
If no real space optimization is selected QCUT must be zero. The default values are:
RMAX 
= 
RCORE 
RDEP 
= 
RCORE 
QCUT 
= 
1, automatic real space optimization 


default cutoff 
QGAM 
= 
2*QCUT 
If real space optimization should be done,
QCUT must be set to the energy cutoff,
which will be used in VAMP. Anyway here QCUT has to be supplied in 1/a.u.
(i.e. as a inverse length)
and can be calculated from the cutoff energy using the formula
If any wrap around errors are omitted in VAMP, QGAM can be 3*QCUT, but
if the 3/4 rule is used for setting up the
FFT meshes (see section 8.4) QGAM must be 2*QCUT.
To get accurate real space projection operators RMAX has to be somewhat large
than RCORE, usually 1.25*RCORE is sufficient.
After the optimization the projection operators have been changed
between QCUT and QGAM, the new projection operators are written
to the file POTCAR in real and reciprocal space. This means
that slightly different results might be obtained if the
real space optimization has been done even if the projections
are evaluated in VAMP in real space (LREAL=.F.). If
the unmodified reciprocal projection operator should be written to
POTCAR set QCUT to a negative value.
Finally there is a default optimization build into fourpot3, which
can be selected by QCUT=1. In this case the pseudopotential
is optimized for the 3/4 FFT meshes, QCUT is set according to
the default cutoff ENMAX and the
RMAX is set to RCORE*1.3.
For further reading we refer to [47].
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N.B. Requests for support are to be addressed to: vasp.materialphysik@univie.ac.at