[gmx-users] acpype generated different tip3p water paramters

Yun Shi yunshi09 at gmail.com
Thu Oct 6 09:17:06 CEST 2011

Hi Alan,

So is acpype using a conversion factor of 4.184 for dihedral force constant?

I found some dihedral constants as 0.156 in the amber format, which should
be 0.156*4.184=0.652704 in gromacs unit. However, acpype gave a force
constant of 0.65084 after conversion, which is slightly off. I wonder if
this is OK, and I suspect it might be that I used rdparm to check the amber
format value, which only gives 3 decimals for force constants.

Thanks for the reply,

>Hi Yun,
>ACPYPE is working fine. What happens here is I choose the >reproduce the
>exact values one sees in AMBER.
>Now why GMX tip3p file choose a different value, I don't know.
>Nevertheless, it's pretty simple to put whatever value you want there >if
>think you need.
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