[gmx-developers] Accurate energy minization is not reliable

[David van der Spoel]

Hi,

I am finding that energy minimization not always succeeds, even for very 
simple molecules such as 2-octanol or pentoxypentane. This leads to 
problems when you want to do a normal mode analysis based on that structure.

The code for conjugate gradients has comments (from Erik) that suggest 
there are some short-cuts being taken (see example below). I do not want 
to modify this code, but it might be good to have a minimizer that 
*does* go all the way to zero force (steepest descents doesn't do it 
either).

Suggestions?


          * In theory, we should minimize the function along this direction.
          * That is quite possible, but it turns out to take 5-10 
function evaluations
          * for each line. However, we dont really need to find the 
exact minimum -
          * it is much better to start a new CG step in a modified 
direction as soon
          * as we are close to it. This will save a lot of energy 
evaluations.
          *


-- 
David van der Spoel, Ph.D., Professor of Biology
Head of Department, Cell & Molecular Biology, Uppsala University.
Box 596, SE-75124 Uppsala, Sweden. Phone: +46184714205.
http://www.icm.uu.se