Subject: re: CCL:curvilinear step not converged in G98-clarifications

From: "Ferber, Steven D" <sferber/at/howard.edu>
Date: Wed, 27 Aug 2003 04:16:54 -0400

Dear Joslyn Kravitz, Shen Cai & anybody else interested,

    I quickly presumed the original question was referring to coordinates
input in CARTESIAN's - after Joslyn's note I went back to see that Shen may
have been working in INTERNAL coordinates => Z-matrix input.
    I work on rather large molecules (Nucleotides ~ 40 atoms) starting from
crystal structures (Cartesians) so I found a way to freeze atoms
accordingly. I ran into the exact same error message as Shen & found this
way around it. 
     Conceptually it may be more tedious - but pragmatic-ly it would work to
re-input your peptide (& associated water molecules) in Cartesians for the
"fake" optimization & subsequent real one as per my first note.

   The real problem may be how to "tether" your hydration molecules to the
peptide as IT optimizes - ya may have to do a quasi-Step opt "crawl" of your
own over a few cycles (i.e. opt the peptide w/hydration frozen, then
vice-versa). A bit "brute force" though it should work - or maybe write a
macro doing the same.

               Steve Ferber
               Howard U. Chemistry
               sferber/at/howard.edu