Define the ion-water interactions

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Dear community,

I am doing a slab geometry of upper and lower Silicon wall with KCl solution in between. (K+: POT, Cl-: CLA)
The interaction between potassium-water (POT-OW) and chloride-water (CLA-OW) is important to my simulation.
Therefore, combine the LJ parameters of POT-OW and CLA-OW to the [ pairtypes ] ffnonbonded.itp in charmm36.ff.

[ atomtypes ]
;type atnum         mass   charge ptype       sigma   epsilon
   SI    14    28.085500    0.000  A  0.3386  	      2.447    ; Gromacs manual 3.0
  POT    19    39.098300    0.000  A  0.3335          0.418371 ;"Atomistic simulation" use
  CLA    17    35.450000    0.000  A  0.4405          0.418371 ;"Atomistic simulation" use
  HW	  1	    1.008000    0.41   A  0.0             0.0 
  OW	  8	  15.999400  -0.8476   A  3.165e-01       6.503e-01     ; Gromacs manual 3.0
[ pairtypes ]
; i    j  func            sigma           epsilon 
  OW   CLA  1  		0.3785           0.5216   ; Koneshan et al. 1998
  OW   POT  1  		0.325            0.5216   ; Koneshan et al. 1998
  OW   SI   1  		0.32755          1.261461 ; Calculated from SI-SI in Gromacs manual 3.0

However, there is no POT-OW and CLA-OW defined in the [pairs] of my topology file.

I would like to know

  1. whether the LJ parameters defined in ffnonbonded.itp is actually been used during the simulation?
  2. Do I need to define the POT-OW and CLA-OW to let Gromacs to calculate the interaction force between them? or Gromacs will automatically calculate it because I set gen-pairs = yes in the [default] of the forcefield.itp?
[ defaults ]
; nbfunc	comb-rule	gen-pairs	fudgeLJ	fudgeQQ
1	2	yes	1.0	1.0
  1. Does the ions.itp have any effect on it?
[ moleculetype ]
; molname	nrexcl
K		1
[ atoms ]
; id	at type		res nr	residu name at name  cg nr	charge	 
1		POT			1		K			K		 1		1

Thank you for reading my questions.
Any comment is highly appreciated.