[gmx-users] about minimization

hugo verli hugo at acd.ufrj.br
Thu Mar 21 20:45:26 CET 2002

Hi to all, 

sorry if I am introducing problems already discussed before in this list. But I
wasn`t able to resolv it yet and I did not found teh answer in the list files. I
read some references in wich the gradient used to normal mode analysis is under
10e-5 kcal. But I cannot achieve gradient under 10e+2 kj, neither with steepest
descents or with conjugated gradients. I reproduced these erros and one answer
here. But I am working with double precision so the problem still exist. I also
tried to minimize another system (I choosed the speptide.pdb from gromacs
tutorial). The error with this structure is the same. Could these errors be dued
to my machine or am I doing something wrong? 

Many thanks to any kind of help,


>>Stepsize too small Converged to machine precision,
>>but not to the requested precision (100)
>>what does this mean?
>This means that with single precision the required tolerance (RMSF of 100)
>can not be reached. THis is usually not a problem, unless you want to do 
>normal mode analysis, but then you need double precision anyway..
>>Negative number for sqrt encountered (-48075003396096.000000)
>>Terminating minimization

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