imaginary frequencies of water dimer even with tight convergence parameters

[lar... at lbl.gov]

I am trying to compute the vibrational frequencies of small water clusters, 
and I am having trouble getting rid of imaginary frequencies, even for the 
water dimer, using very tight convergence parameters during the geometry 
optimization.I have also tried to run the simulations with periodic 
boundary conditions, different values of the displacement, etc., but I 
still get a few imaginary frequencies. I have run out of ideas to try so 
any advice will be greatly appreciated. I have attached here the input 
files of the calculations. 

Thanks for your time!
Luis
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