[gmx-users] Hamiltonian replica exchange not working in 4.6

[Sanku M]

Dear Gromacs user,
  I am not sure whether this is any potential bug. But I found that in gromacs4.6.3, hamiltonian replica exchange simulation is not
working. The SAME simulation works perfectly fine in gromacs 4.5.4
But, when I try to run the simulation using gromacs4.6.3, I get following error:
"The properties of the 10 systems are all the same, there is nothing to exchange
For more information and tips for troubleshooting, please check the GROMACS"


Here is the details on the error:
   I have first defined A and B state by scaling the relevant parameter.. Then I have  generated different tpr file by using mdp file which only differ by 'init-lambda' parameter:
For example, I have 10 different mdp files: Free energy part of two of them are shown below:
for hremd0.mdp, the relevant part for free energy part is 
  ; Free energy control stuff
free_energy  = yes
init-lambda              = 0
delta_lambda = 0

for hremd1.mdp
; Free energy control stuff
free_energy  = yes
init-lambda              = .080
delta_lambda = 0
..
and so on..
The rest of mdp portions are same for all the mdp files...



However, with gromacs4.5.4, the same simulation works without problem. I do not get the error that all the systems are identical.

In both cases, I am using same system with OPLS forcefield.. 
The way I run the simulations is:
mpirun -np 10 mdrun_463 -multi 10 -v -s hremd -replex 250 -c &>log_repl


Any help will be appreciated.

Sanku