initial hesse matrix

[noertema ( ( at ) ) theochem.tu-muenchen.de (Folke Noertemann)]

 Dear Colleagues,
  in order to set up an initial hesse matrix for geometry optimizations
 built up from a simple valence force field (see e.g. H.B.Schlegel,
 Theoret.Chim.Acta 66,333,(1984)) I have written a  short routine
 that establishes valence coordinates from a given set of
 cartesian coordinates. Whether there is a bond or not between
 a pair of atoms is determined by a set of covalent radii
 and two parameters which I have taken from a piece of code
 written by T.A.Halgren ('NABOR').
 Since I have no idea how old this piece of code might be, I would
 like to know if there is a standard set of covalent radii somewhere
 and perhaps also a standard rule which tells me if there is a bond
 between two atoms or not using these covalent radii.
 Thank you very much in advance,
    F.Noertemann
 Folke Noertemann
 Lehrstuhl f. Theoret. Chemie
 TU Muenchen
 Lichtenbergstr. 4
 85474 Garching