"INTC" Program Documentation

new version, Nov. 13, 1995

    Given a cartesian coordinate file, program INTC generates the
corresponding internal coordinate file according to Pulay's definition.
H atom must come in the end of cartesian coordinate, if there's H in the
molecule.

 type  coordinate type: stre, invr, bend, out, tors, lin1, lin2

 a,b,c,d  participating atoms

 stre  stretch coordinate, order of a and b arbitrary
 invr  inverse stretch?, order of a and b arbitrary
 bend  bond angle deformation, a and b are end atoms, c is the apex atom
 out   out-of-plane deformation, atom a out of the bcd plane, c is the
       central atom, coordinate is positive if a is on the same side of
       the plane as the vector product db*bc. b and c can be exchanged
       but this changes the sign of the coordinate.
 tors  the coordinate is defined as the angle of the planes abc and bcd.
       Note that abcd and dcba are equivalent; the sign of the torsion
       does not depend on the direction of the numbering. Note that the
       value of the coordinate varies between -pi/2 to 3pi/2, not between
       -pi/2 to pi/2
 lin1  colinear bending of the linear chain of atoms a-c-b in the plane
       which contains d. The sign is positive if a and b move towards d.
 lin2  is the perpendicular linear bending. It is positive if a ad b move
       in the direction of the vector product cd*ca.
                                                              

Files:

(in)
intcin(5)      standart input

(out)
Intcoor(7)     internal coordinate file in capital
intc.out(17)   listing file
force(8)       force file
fdiag(9)       diagonal hessian file


                             **************
			     * User Input *
			     **************


1) TEXAS TITLE         the first 5 characters being 'TEXAS', FORMAT(A80)

2) DO I = 1, NATOM
      NAME(I), IAN(I), X(I), Y(I), Z(I)
   ENDDO
   NAME: atom label
   IAN : atomic number
  X,Y,Z: cartesian coordinate
  FORMAT(2x,A2,6X,4F10.5)
** if there's H atom, it must be in the end. **

3) Using OPTIONS:

   options must be defined  immediately AFTER the
   atomic coordinates;

   (note for implementation: these options are read by
   the subroutine INTC itself, while the standard input
   above is for the driver program main)

   each option is on a separate line
   they are in arbitrary order (except that in case of
   RADI(below), the lines specifying individual radii
   must be at the very end).
   Only the first 4 characters are relevant,
   you may use longer keywords,
   ( e.g. NOOFFSET for NOOF below)

   B631 - offset forces will be produced referring to
     to 6-31G* basis, rather than the default 4-21(*)

   NOOF - no offset forces at all will be punched

   NOFD - no force constants will be punched


     A SPECIAL option, use it WITH CAUTION:

       In some special cases, you may want to change
     the atomic radii that define whether an atomic
     pair is considered as bonded or not. (The definition
     of natural coordinates will depend on this!)

     This can be done in two different ways:

     a) blowing up all radii uniformly:

     BLOW      blowfact       (format A4,6X,F10.5)

     all radii will be multiplied  ( in subr BONDS )
     by blowfact (this overwrites the default value of 1.25)

     b) changing individual radii:

     RADI      n.        (format A4,6X,F10.)
     i1.       r(i1).    (format 2F10.5)
     i2.       r(i2).
     .....
     in.       r(in).

     the radii of n atoms, defined by the serial numbers
     i1,....in will obtain  the new values given. n pairs
     of data are read (note that in this case the default
     blowfactor of 1.25 is still also working on each atom)


                              ************
			      * Examples *
			      ************

Linear molecule NEEDS DUMMY atom( ie. with zero charge):

TEXAS        acetylene by hand, with dummy
N=C       6.        -0.6
N=C       6.        +0.6
N=H       1.         -1.6
N=H       1.         +1.6
N=DU      0.          0.          10.