[gmx-users] Anomalous temperature

[zhongjin]

Dear gmx users,
 
   It seems that I have found a strange temperature value after NVT equilibrium for 200 ps. I simulate a CNT with two graphite sheets in water box. I do not want to them to deform or change their shaps, So I use a very large position restraint (1*10^6) to keep their shaps. The temperature was set to 300 K, but after NVT equilibrium, the tempertaure was 330K.
 
.mdp content
define                   = -DPOSRES_CNTGATE -DPOSRES_K -DPOSRES_CL
; OPTIONS FOR WEAK COUPLING ALGORITHMS
; Temperature coupling  
tcoupl                   = v-rescale
nsttcouple               = -1
nh-chain-length          = 1
; Groups to couple separately
tc-grps                  = Other Water_and_ions
; Time constant (ps) and reference temperature (K)
tau-t                    = 0.1 0.1
ref-t                    = 300 300
 
results
Energy                      Average   Err.Est.       RMSD  Tot-Drift
-------------------------------------------------------------------------------
Temperature                 331.548        2.6    10.3739    15.0042  (K)
T-Other                     436.927         12    39.4112    67.2519  (K)
T-Water_and_ions            303.349       0.16    6.07417    1.02328  (K)
 
the Other, that is CNT and two graphite sheets temperature is very high!!!
 
Howerver when I freeze them, the temperture is OK
 
freezegrps               = K CL Other
freezedim                = Y Y Y Y Y Y Y Y Y
 
the results is

Energy                      Average   Err.Est.       RMSD  Tot-Drift
-------------------------------------------------------------------------------
Temperature                 299.998     0.0034    4.84173 -0.0066645  (K)
T-Other                           0          0          0          0  (K)
T-Water_and_ions            299.998     0.0034    4.84173 -0.0066645  (K)
 
So I should freeze them or use a small postion restraint to constaint them, in order to get the correct temperture?
 
Zhongjin He
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