MM simulation for orthorhombic box of water?

[Rahul Hardikar]

Dear cp2k Experts/Users,

Recently, I have come across a issue while simulating liquid water in an 
orthorhombic box where cell lengths in X (11 ang) and Y (9.6 ang ) 
directions are similar and the C (110 ang) length is about 10 times that of 
X and Y. When I run a MM simulation with SPC/E parameters and constraints 
for OH distances, I end up with a blob/slab of water with density as high 
as 2 gm/cc. By the way, the same set up works perfectly for a cubic box. 
>From what I understand, parameters such as alpha and rcut need to be 
optimized for the electrostatic interactions to be reproduced correctly. My 
observation so far is that low value of alpha  < 0.1 ang^-1 and rcut of 4.8 
ang with SPME although does not reproduce ideal results (RDFs) for liquid 
water, at least prevents the water to collapse into and give very high 
density as mentioned before.  

My question to the experts is whether there any issue with the setup or am 
I missing some important point that will influence the MM simulation. Also, 
how can I test optimal parameters for SPME that can give correct 
electrostatics and reproduce accurate density of liquid water. 

Thanks in advance!
Regards,
Rahul
 

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