[gmx-users] buckingham & pairs

[Luca De Gaetani]

I'm trying to use the Buckingham potential in my simulation. First, I've 
selected

 [ defaults ]
 ; nbfunc   comb-rule   gen-pairs  fudgeLJ  fudgeQQ
     2               2               no          0.0            0.0

and then in atomtype I've put A,B,C as needed by that potential.
But I have some problem in the "pairs" section. Infact I have specified 
all my pairs as:

 [ pairs ]
 ;  ai    aj
   2      26    1     0.330  0.69

i.e. 0.330 and 0.69 are standard Lennard Jones terms.
The problem is that the LJ-14 energies with Buckingham active (nbfunc=2) 
is different from that of the same system (same INTRA molecular part, 
different INTER molecular). They should perfectly agree, so the 
difference is in the function used to calculate the intramolecular 
potential with different nbfunc.
 So, what kind of functional is used in [pairs] within the Buckingham 
system?
Thank you
Luca