Relative entropy error

[Erez Tamir]

Dear all,

I'm trying to apply the relative entropy (RE) method, with LJ 12-6 interactions, for polymer melt containing 8 bead types.

My final goal is to reproduce mechanical properties of the atomistic system by CG potentials.

In order to obtain reasonable initial guess I used the IBI method with pressure correction until the target density and pressure obtained.

The mechanical behavior is underestimated by the IBI potentials, so I would like to improve them by fitting and optimizing LJ 12-6 potentials with the RE method.

Each IBI potential was fitted by lj126 function and the obtained parameters are the initial guess.

I understand that the lj126 functional  in votca is of the form: U(r)=(A/r^12)-(B/r^6), so A=4*ε*σ^12 and B=4*ε*σ^6. Is this correct?

Following this my RE input for example for ε=2.1Kcal/mol and σ=4.8A is:

#xy

0 1256533682

1 102737

The following error message appears during iterations: 

an error occurred:

Hessian NOT a positive definite!

This can be a result of poor initial guess or ill-suited CG potential settings or poor CG sampling.

Is this error due to incorrect input or poor initial guess?

The settings file is attached.

Any help will be appreciated.

Best,

Erez

[Christoph Junghans]

Sikandar knows the details better than me, but I believe this error
usually means you didn't sample long enough in the iteration step and
hence the hessian is not positive definite.

Christoph

> The settings file is attached.
>
> Any help will be appreciated.
>
> Best,
> Erez
>

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Christoph Junghans
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