[gmx-users] REMD Showing Zero Exchange Probability

[Ligesh Lichu]

Dear all,
    I have performed REMD for a system containing Protein, Reline, Urea and
Water in the temperature range 290 to 450 K consist of 16 replicas out of
47 replicas generated by REMD temperature generator. But after the MD
simulation the exchange probability is zero. I have used position
restraints for reline, urea and protein. Is there any chance that position
restraints  cause the exchange probability to be zero?  I have one more
query that, the REMD temperature generator produced around 45 to 54
replicas for my system in the required temperature range. But I have only
80 processors to do the job, So is it necessary to choose the consecutive
temperature replicas given by the REMD temperature generator or I can skip
some temperatures in between?

If I am using the equation *Ti = T0 exp (k* i)*, what determines the value
of 'k'  how it affects the exchange probability? How can I choose the value
of 'k' for an arbitrary system?

Thanks in advance...