Charged clusters - zeolite anion

[ajones]

Hi,

I am trying to calculate the energy of an anionic zeolite cluster in order to calculate the deprotonation energy (DPE) of the zeolite (HZ -> H+ + Z-).

I am using a large supercell (288 atoms for MFI type zeolite) but am obtaining very large values for the DPE (1600 kJ/mol instead of the expected 1200 kJ/mol which has been calculated using QM/MM methods, the only reference using periodic DFT to calculate DPE I know of is using CPMD 'Trout, J. Catal. 227 (2004) 77', but this should be a trivial matter for VASP, right?). I specify NELECT which is larger than for the neutral system, and use:
IDIPOL = 4
LDIPOL = FALSE
LMONO = FALSE/TRUE (tried both, not a big difference)

The structures converge but the energy of the anion is -2283 eV which is more positive than expected. This is similar to the issue by lux (http://cms.mpi.univie.ac.at/vasp-forum/ ... php?4.5731) that was not solved.
Thanks

[support_vasp]

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