[gmx-users] free energy and tabulated potentials, free energy and Ewald ?

Michael Brunsteiner mbx0009 at yahoo.com
Fri Jan 30 10:31:00 CET 2004

dear gmx-user,

two questions:

1) Can somebody tell me whether free energy calcs (TI)
can be done in combination with user defined tabulated
potentials ? ... is this implemented in gmx-3.2 or 3.1.4
and do I get the correct dU/dlambda ?

2) dU/dlambda is not calculated for the reziprocal part of the Ewald
sum when doing TI, did anybody try to calculate an approximation
to dU_Ew^rezip/dlambda by setting the charges of part of the system 
zero and doing a rerun to get the U_Ew^rezip (lambda) contribution
to the interaction energy ? If one calculates the lambda-derivative
from U_Ew^rezip (lambda) for a series of lambda values numerically
how large (approximately) is the error introduced ?
This problem was discussed previously in this list and I seem to
recall that one of the developers wrote that they were working
on it, this feature is not yet implemented in 3.2, is it ?


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