[gmx-users] Tabulated soft-core potential, Ewald and free energy

[Filip Ryjácek]

Hi all,
I am using soft-core approach for free energy calculation in GORMACS (works 
wery well, comparing to AMBER/gibbs for example!), and I have encountered 
two problems:

a) As show in output and in do_fnbf() and do_14(), GROMACS has only 
tabulated routines for free-energy coulomb and LJ interactions (inl3301 and 
inl3302). In manual v3.1.1 on page number 122 is written: "Note that table 
lookup is significantly slower than computation of the most simple LJ and C 
interaction". So I guess GROMACS is slower for free energy calc. than for 
mol. dynamics! Is there any technical/theoretical reason for that?

b) I don't understand exactly the 'FEP_TABLE_LENGTH' variable. Why is it set 
to 5nm? Is it something like cutoff?

Thanks for the help!
Filip







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