MM simulation for orthorhombic box of water?

[Marcella Iannuzzi]

Dear Rahul, 


what did you specify for GMAX in the EWALD section?
Having such a difference among the cell's sides, you probably need 
different GMAX values in the different directions
Best,
Marcella


On Friday, June 9, 2017 at 6:47:21 AM UTC+2, Rahul Hardikar wrote:
>
> 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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