RIGID DYNAMICS problems--please help

Rebecca Page rpage at MOSES.PRINCETON.EDU
Thu Feb 5 12:22:34 EST 1998


Hello Xplor users!

I am a new user to xplor and I am having trouble with
RIGID DYNAMICS.  Specifically, I am using the following
dynamics scheme:

        evaluate ($init_temp=300)
        vector do (vx=maxwell($init_temp)) (all)
        vector do (vy=maxwell($init_temp)) (all)
        vector do (vz=maxwell($init_temp)) (all)

        constraints interaction = (store5)=(store5) end
        dynamics rigid
          nstep=1000
          dt=0.005
          group=(residue 1:76 or residue 140:275)
          group=(residue 86:130)
          dynmode=tcou
          tbath=298.
          nprint=5
          ntrfrq=1
        end

        (where store5 is just 1:76 or 86:130 or 140:275.)

I have tried a number of variations on this scheme--
including weak harmonic constraints, changing the init_temp,
including/excluding various energy terms, but every time
I run it, the molecule 'blows up' (atoms not found...)
and the job crashes.  I have noticed from my output that
the 'blowing up' correlates with an increase in the reported
temperature.  For example:

-------- step=   135 at      0.67500 ps -------------------------
 | E(kin)+E(total)=0.75E+11        E(kin)=0.59E+11
                                        temperature=0.49E+13   |
 
| Etotal =0.17E+11   grad(E)=0.11E+06   E(BOND)=0.49E+10
                                        E(ANGL)=5343.066   |
 
| E(DIHE)=6020.615   E(IMPR)=457.104    E(VDW )=-1193.301
                                        E(HARM)=0.12E+11   |

 |
E(PVDW)=0.000                                                              
|

-------------------------------------------------------------------------------

(This was the last energy step before the job crashed.
I thought I was "fixing" the temperature to 298 when I used the command:

        tbath=298.
)

If anyone can tell me how the energy (temperature) is
calculated/controlled
in tcoupled dynamics and can give me any suggestions on how to do a
rigid dynamics run
without having the molecule blow up, I would sincerely appreciate it.


Thanksin advance!

Rebecca Page

**********************************************************************
Rebecca Page			email:	rpage at ace.princeton.edu
Graduate Student		phone:	(609) 258-2827
Chemistry Department		fax:	(609) 258-1980
Princeton Univeristy
**********************************************************************



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