[QMMM] H trapped in QM atoms when the QM region has negative charge (ECOUPL GAUSS)
Shawn Yang
shawn.yan... at gmail.com
Wed Jan 10 03:11:16 UTC 2018
Dear CP2K user,
Recently I am using QM/MM to do some MD calculations, the box include a
negative QM box and MM water solvents, therefore the net charge is -1. For
example, only CO2- in the QM region surrounded by TIP3P water. As far as I
understand from the Laino's work in 2005, this unphysical problem has been
solved by using a finite width density of charge on MM atoms.
However, the MM proton still trapped into the quantum oxygen atoms, and MM
oxygen, also trapped into quantum carbon atom. The input for my QMMM part
is attaed below, any suggestions would be appreciated.
PS. When I test in pure water bulk (QM water + MM water) system, the result
doesn't have this problem. So I guess if I could increase the width of MM
atoms? Or apply an artifical replusive potential to avoid the trap?
Many thanks for your help!
Xiaohui
&QMMM
&CELL
PERIODIC NONE
ABC [angstrom] 10 10 10
&END CELL
&WALLS
TYPE NONE
&END WALLS
&PERIODIC
GMAX 0.5
&POISSON
PERIODIC NONE
POISSON_SOLVER MULTIPOLE
&END
&MULTIPOLE ON
EWALD_PRECISION 1.0E-6
RCUT 26
&END
&END PERIODIC
&QM_KIND C
MM_INDEX 1
&END QM_KIND
&QM_KIND Oq
MM_INDEX 2 3
&END QM_KIND
&MM_KIND H
RADIUS 0.44
&END MM_KIND
&MM_KIND O
RADIUS 0.78
&END MM_KIND
E_COUPL GAUSS
USE_GEEP_LIB 10
NOCOMPATIBILITY
&END QMMM
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