[gmx-users] Parameterising for a Solvent

[David van der Spoel]

On Tue, 2003-09-02 at 09:30, Dallas Warren wrote:
> Thank you for the replies Eric and David.
> OK, having done that now:
>         Eintra(gas) = 55.4815
>         RT = 2.4776
>         [Eintra+Einter](liquid) = 14.747
>         DHvap = 43.21           versus 58.0
> 
> Now that is much more reasonable.  Not perfect, but at least in the
> ball park now.
You're saying that it is 14.7 kJ/mole off? Hmm, what molecule is this?

What you may need to do is to increase the dipole (like e.g. spc water
has 2.25 iso 1.85) to account for polarisation. You can actually
optimize the parameters during an MD simulation by coupling the
parameters to the energy and the pressure. Since there are two
observables you have two degrees of freedom, i.e. you can scale the
charges to account for higher DHvap, and one of the C12 parameters to
get the pressure right. See e.g. JCP 108 pp. 10220-10230 (1998) and 
JPC B. 105 pp. 2618-2626 (2001) (pdfs available from my website below)


-- 
Groeten, David.
________________________________________________________________________
Dr. David van der Spoel, 	Dept. of Cell & Mol. Biology
Husargatan 3, Box 596,  	75124 Uppsala, Sweden
phone:	46 18 471 4205		fax: 46 18 511 755
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://xray.bmc.uu.se/~spoel
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