Outside of grid - Error with Funnel MetaD

[Mercè Alemany]

Hello plumed developers and fellow users, 

I have been using funnel WT metadynamics to study the encapsulation process of a small molecule into a metallocage. I have 2 systems, same metallocage but different ligands. I find myself stuck as I get the following plumed error:

```

PLUMED: ################################################################################
PLUMED:
PLUMED:
PLUMED: +++ PLUMED error
PLUMED: +++ at Grid.cpp:169, function PLMD::GridBase::index_t PLMD::GridBase::getIndex(const std::vector<unsigned int>&) const
PLUMED: +++ message follows +++
PLUMED: ERROR: the system is looking for a value outside the grid along the 0 (fps.lp) index!
PLUMED:
PLUMED: ################################################################################

```

This error does not appear right when I lauch the calculation but at some point during the calculation. Sometimes it is the fps.lp value that triggers the error, but other times it is the fps.ld. These two facts confuse me a bit as I don't understand why they happen.

I have been playing with the plumed input file, the funnel parameters, its position, orientation and every other aspect I have thought of, but I have run out of idees.

I  attach here the input file I have been using:

```

RESTART

box: GROUP ATOMS=1-280
lig: GROUP ATOMS=281-312
anchor_atom: GROUP ATOMS=280

WHOLEMOLECULES ENTITY0=box ENTITY1=lig

WRAPAROUND ATOMS=lig AROUND=anchor_atom

cbox: COM ATOMS=1-280
clig: COM ATOMS=281-312

fps: FUNNEL_PS LIGAND=clig REFERENCE=ref_ga.pdb ANCHOR=280 POINTS=2.968,2.630,5.233,3.889,2.826,4.726 NOPBC

funnel: FUNNEL ARG=fps.lp,fps.ld ZCC=4.0 ALPHA=0.25 RCYL=0.10 MINS=0.0 MAXS=4.5 KAPPA=35000 NBINS=500 NBINZ=500 FILE=BIAS_NoProt

d: DISTANCE ATOMS=cbox,clig

metad: METAD ARG=d SIGMA=0.03 HEIGHT=0.3 PACE=500 TEMP=298.15 BIASFACTOR=10 GRID_MIN=0 GRID_MAX=3 CALC_RCT FILE=HILLS_NoProt

fuwall: UPPER_WALLS ARG=fps.lp AT=4.0 KAPPA=35000 EXP=4 OFFSET=0
uwall: UPPER_WALLS ARG=d AT=2.0 KAPPA=1500 EXP=4

PRINT STRIDE=100 ARG=d,metad.bias,uwall.bias FILE=COLVAR_NoProt

```

I have watch the masterclass about funnel metadynamics, and have tried all options proposed in this google group for this error. Nothing has worked for now, and I am open (maybe even a bit desperate?) for suggestions.

I would like to understand what is causing it, why it happens and what I can do to fix it.

I will appreciate any help you may give me,

Thank you!

Mercè