Hu Zhongqiao wrote:
Dear Mark
Thanks for your reply.
In more detail, I used ffg43a1 force field. In the file ffG43a1nb.itp,
one can find the Lennard-Jones parameters for Na+ as follows:
C6=7.2063121e-05; and C12= 2.1025e-08
From these 2 values one can get epsion(Na+)=0.0617 kJ/mol.
Because the force field parameters for ions is relatively simple, the
main interaction of Na+ with other particles is electrostatic and van
der Waal's forces. And I also believe that the combination rule makes
not big difference for different force fields in this case. It is
strange epsion(Na+) = 0.0617 kJ/mol in ffg43a1 is very different from
some references (for example, in the paper shown in my last email, this
value is epsilon(Na+) = 0.42 kJ/mol ).
This is not strange at all. These force fields are probably optimized to
achieve different targets under different simulation conditions on a
different test set. There is no wonder that they are different, and
there's no particular expectation of correlation with any property of
real Na+. Ensemble average properties of systems with solvated Na+
should be reasonable, however.
So I just want to know how the
developers of gmx or gromos force field get Lennard-Jones parameters for
Na+.
You should find the original literature that describes them and read it.
That's why the authors wrote it :-)
Mark
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