Charge Vacancy Calculation Error

[tommy91779]

Hello all,

I am doing a set of vacancy calculations for an AX system where A has 12 electrons and X has 6 electrons. Considing a 3x3x2 supercell, I have 36 AX pairs which gives 648 electrons. For a neutral X vacancy I of course have 642 electrons. I would now like to perform a 1+ charged X vacancy calculation. I set the flag NELECT=641. UNfortunately when I perform the calculation, I obtain the following error:

LDA part: xc-table for Ceperly-Alder, standard interpolation
POSCAR, INCAR and KPOINTS ok, starting setup
WARNING: wrap around errors must be expected
FFT: planning ... 4
reading WAVECAR
WARNING: random wavefunctions but no delay for mixing, default for NELMDL
entering main loop
N E dE d eps ncg rms rms(c)
DAV: 1 0.322421237694E+04 0.32242E+04 -0.21631E+05 18008 0.916E+02
DAV: 2 -0.335114282016E+02 -0.32577E+04 -0.31628E+04 19704 0.281E+02
DAV: 3 -0.246281923418E+03 -0.21277E+03 -0.21077E+03 20008 0.679E+01
DAV: 4 -0.249997819101E+03 -0.37159E+01 -0.36964E+01 19648 0.816E+00
DAV: 5 -0.250072145117E+03 -0.74326E-01 -0.74188E-01 19912 0.946E-01BRMIX: very serious problems
the old and the new charge density differ
old charge density: 642.00000 new 641.00001


BElow is my INCAR file

Electronic minimisation
IBRION = 2
ISIF = 2
NSW = 300

LREAL = Auto

NELECT = 641



Does anybody have any insight into my particular problem??


Thanks in advance

-Tom

[admin]

this actually is no error: for the initial 5 steps, vasp just 'initializes' the Hamiltonian and the wavefunctions from the POTCAR file (without any charge update, i.e ignoring the NELECT tag).
After the 5th electronic step, NELECT is recognized to be different from the sum of valence electrons as calculated from POTCAR.
The written 'warning' just tells you about this (cell is not charge-neutral), vasp will continue to run for 641 valence electrons.
please keep in mind that for charged systems, it may improve convergence to add set IDIPOL (and even apply multipole corrections, please have a look at the respective chapter of the online manual)