Subject: Determinant of Hessian matrix

From: [email-masked] (Taesung Moon)
Date: Wed, 13 Nov 1996 14:43:47 -0800

Dear netters,

I have tried to evaluate the determinant of Hessian matrix evaluated 
using Discover3.0. The Hessian is positive definite at minimun 
conformation but some determinants are negative in my cases. 
I carried out full minimization using Quasi-Newton 
or Newton-Raphson method until maximum derivative is less than 0.00001.

For example,
---------------------------------------------------------
                      the determinant of Hessian matrix
                      ----------------------------------
 method               butane           alanine dipeptide
---------------------------------------------------------
Quasi-Newton          negative            positive
Newton-Raphson        positive            negative
---------------------------------------------------------

Please let me know the reason. 

Thanks.

-------------------------
[email-masked].

---

From: A J Turner <[email-masked]>
Date: Mon, 18 Nov 1996 09:02:54 +0000 (GMT)

Hi!

There are too resons that I can think of.  First - the optimiser is not
finding a minimum.  I cannot say much on this - as I do not know the
particular implementation.

Second - the hessian is nearly singular - and the numerical noise is
causing negative eign values to turn up.

My I suggest reoptimisation of the stationary points which you have
obtained - using a first order (conj grad or sd) method.

Hope it helps

Alex

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|Alexander J Turner         [email-masked]                  |
|Post Graduate              |http://www.bath.ac.uk/~chpajt/home.html|
|School of Chemistry        |+144 1225 8262826 ext 5137             |
|University of Bath         |                                       |
|Bath, Avon, U.K.           |Field: QM/MM modeling                  |
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