[gmx-users] Problem to run more than 2 NPT REMD replicas

[pascal.baillod at epfl.ch]

Dear REMD users and developers,


I still do not manage to get PT running with more than 2 replicas, in the
NPT ensemble.. For reminder:

I have tried running NPT-REMD with 3 replicas, at 300, 302 and 304 K. My .mdp
files are identical, with the exception of the target temperature. I
systematically get the following error message:



++++ PLEASE READ AND CITE THE FOLLOWING REFERENCE ++++
T. Okabe and M. Kawata and Y. Okamoto and M. Mikami
Replica-exchange {M}onte {C}arlo method for the isobaric-isothermal ensemble
Chem. Phys. Lett. 335 (2001) pp. 435-439
-------- -------- --- Thank You --- -------- --------
                                                                               
                               
Multi-checking the number of atoms ... OK
Multi-checking the integrator ... OK
Multi-checking nsteps ... OK
Multi-checking init_step ... OK
Multi-checking the temperature coupling ... OK
Multi-checking the number of temperature coupling groups ... OK
Multi-checking the pressure coupling ... OK
Repl  There are 3 replicas:
Repl      0     1     2
Repl  T 300.0 302.0 304.0
Repl  p  1.00  1.00  2.00-------------------------------------------------------
Program mdrun_mpi, VERSION 3.3
Source code file: repl_ex.c, line: 142
                                                                               
                               
Fatal error:
The reference pressure decreases with increasing temperature
-------------------------------------------------------
                                                                               
                               
"Smileys are Not Cool" (D. Van Der Spoel)


As you can see from the log file above, I set the target pressure from the 3rd
replica to 2 bar, just to check out the "fatal error" statement. As additional
tests, I 

1) prepared the tpr files after removing the pressure keywords in the .mdp input
files, in order to try NVT REMD. This worked out fine, for the same initial
replicas.

2) Tried the same for a small peptide solvated in water, where the replicas were
already pre-equilibrated to the target tempertature. This gave the same error
message. 

Below, follows a copy of one of my 3 .mdp files, the other 2 being identical
with the exception of the target temperature and/or target pressure.


title                    =  
cpp                      = /lib/cpp
include                  = -I../top
define                   = 

integrator               = md
dt                       = 0.0015
tinit                    = 0.0     
nsteps                   = 2000000  
comm_mode       	 = Linear               
nstcomm                  = 1       5
comm_grps                = Protein Other
nstxout                  = 5000             
nstvout                  = 5000                    
nstlog                   = 10 		      
nstenergy                = 10 		
nstxtcout                = 500           
xtc_grps		 =              
energygrps               = Protein Other


nstlist                  = 10
ns_type                  = grid
rlist                    = 1.0
coulombtype              = PME
rcoulomb-switch          = 0
rcoulomb                 = 1.0
rvdw                     = 1.0
fourierspacing           = 0.12
fourier_nx               = 64
fourier_ny               = 64
fourier_nz               = 64
pme_order                = 4
ewald_rtol               = 1e-5
ewald_geometry           = 3d
epsilon_surface          = 0
optimize_fft             = no

tcoupl                   = berendsen
tc-grps                  = Protein Other  
tau_t                    = 0.1     0.4   
ref_t                    = 300.0  300.0
Pcoupl                   = berendsen
pcoupltype               = isotropic
tau_p                    = 1.0
compressibility          = 4.5e-5
ref_p                    = 1.0

constraints              = none   
constraint_algorithm     = 
unconstrained-start      = 
shake_tol                = 1e-04
morse                    = no

gen_vel                  = no


Dose anybody have a clue of what is going on? Many thanks in advance!


Pascal




*******************************************************************************
Pascal Baillod (PhD student) 
*******************************************************************************
Swiss Federal Institute of Technology EPFL	        Tel: +41-(0)21-693-0322
Institute of Chemical Sciences and Engineering ,	Fax: +41-(0)21-693-0320
Laboratory of Computational Chemistry and Biochemistry	pascal.baillod at epfl.ch
Room BCH 4121, Avenue Forel,	                        http://lcbcpc21.epfl.ch
CH-1015 Lausanne	
*******************************************************************************