Void Formation in MM region

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k.watson14
Void Formation in MM region

Hi all,

I am struggling to generate optimised files in ChemShell which do not form voids in the active MM region. I am calculating a metal ion in NaCl. The metal ion has a LanLD2Z PP and associated basis set and the Na and Cl ions have a 6-31G basis set. I am using Gaussian and DL_POLY.

I have run MD simulations and cut clusters from those, which are then optimised within ChemShell. The MD simulations have bond lengths and densities which align with experimental results. I use the MD parameters in the ChemShell calculation.

The QM region contains the metal ion, first solvation shell of chlorine ions, then the closest sodium ions to neutralise the QM region totalling about 4 Å. The active MM region goes from 4-8 Å, with a final region of frozen MM ions 8-10 Å.

Has anyone seen voids in calculations, and how can they be prevented?

Thanks
Ken Watson
PhD Student Imperial College London

david_gunn
Re: Void Formation in MM region

Hi Ken,

Have you tried a purely MM optimisation of the ChemShell cluster (without metal ion) to see if this still forms voids? This would help to give us a clue as to whether the problem is in the forcefield or if there's some kind of mismatch with the QM region.

Thanks,

David.

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