[gmx-users] bond stretching constants in ffgmxbon.itp

[B. Nick]

Dear all,

I want to implement NERD united atom force
field constants in the ffgmx force field.
The values I calculated from literature are
all close to the CH2 parameter of the ffgmx
force field. BUT the bond strechting constant
is about a factor 1000 off. (From Kb=96500K/A^2 given
in the paper I calculate 802,35 kJ/mol A^2, by multiplication
with kB. This is ok for the other constants. But the
ffgmx entry for CH2 CH2 is 334720.)

Aren't the units in the force field table for Kb, kJ/mol A^2 ?

Do I still have to divide the force constant given in the table
by two to get the energy as given by the formular 4.33
in the manual?

Thanks for any help,
Gitta



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Birgitta Nick
DWI an der RWTH Aachen, Germany