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Hello Jie-rong--

> 
> Thank you very much for your reply.  I am not sure if I understand you
> correctly. Do you mean the final temperature of cooling should be room
> temperature (e.g. 298K) instead of 25K in the script? And the high
> temperature dynamics at 3000K and cooling starting from 3000K are not changed
> in my case?  
> 

To start with, just leave the temperatures alone- let's see how large
an ensemble is needed for convergence.

> Why does the script start from a folded structure instead of extended one? Is
> that because there are some "high temperature" steps which can randomly
> expand the structure, and therefore it doesn't matter the starting structue
> is folded or expanded? 
> 

A best initial guess was used in this case. Wildly divergent, expanded
conformations were not sampled.

> Since I only have PRE data, I commented out "NOE", "dihedral angle
> restraints", "repulsive restraints for EDTA-DNA phosphate", "planerity
> restraints", and "base-base positional database", and related parameters
> (e.g.k_noe) as well.

sounds good. You may want the RAMA term. Remove the setup in the .py
file, and replace it with:

#Rama torsion angle database
#
import protocol
protocol.initRamaDatabase()

>  Now I am struggled, final lines in the log file is:

there may be two problems here.

1)

> test.py(569):          s.run()
> *--- Dynamics ---- step=      0 ---- time=         0 ---- delta_t=     0.002
> --*
> | E(kin)+E(poten)=     21110.576 E(kin)=      4449.966 temperature=  
> 3238.358 |
> |   E(poten)= 16660.6104132       grad=           nan      ANGL=   

something's wrong with the gradient. Please remove potential terms one
at a time to figure out which is causing the nan. I suspect a PRE term.

2) 


> InternalDynamics::step: caught assertion failure:
>    calcD_G: singular D matrix. Bad topology?

There may also be a topology problem caused by a bad setup of the
IVM. Let's fix problem 1) first, though.

best regards--
Charles
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