[molpro-user] attempting to define a jacobi coordinate system: zmat error

[Dave Moore]

Hi Mario,

It is generally a bad idea to have the first 3 atoms of a Z-matrix be
colinear.  You can fix this by adding a second dummy atom to the Z-matrix
like so:

q1
q2 q1 1.0
n  q1  rn  q2 90.0
h  q1  rh  q2 90.0    n 180.0
he q1  rhe n theta(i) h   0.0

This provides a well-determined Z-matrix for all possible values of the
jacobi variables.  Note that the value of the dihedral angle in the last
line doesn't really matter, since the last 3 atoms in that line (q1, n and
h) must always be colinear according to the rest of the zmat specification.

Also note that you may want to explicitly specify the symmetry for this
system, since when theta is 0 or 180, the calculation will use C2v, but for
all other values of theta, it will use Cs.

Hope this helps,

Dave Moore

-----Original Message-----
From: owner-molpro-user at molpro1.chem.cf.ac.uk
[mailto:owner-molpro-user at molpro1.chem.cf.ac.uk]On Behalf Of mario
Sent: Monday, 02 May, 2005 12:49
To: molpro mailing-list
Subject: [molpro-user] attempting to define a jacobi coordinate system:
zmat error


Dear Molpro users,

I'm very new in molpro way-of-life ( I started to use it some days ago
). I'm trying to define a jacobi coordinate  system for the NH-He
molecular system using a zmat like this:

geometry={ang,z;   ! distance in angstrom, force planar geometry
q1;          ! dummy center in the center of mass (CM) of NH molecule
n,q1,rn;
h,q1,rh,n,180;
he,q1,rhe,n,theta(i),h,0,0}
rnh=1.0803
rhe=4.000
theta=[0.00,10.00,30.00]
rn=rnh*1/16
rh=rnh*15/16

for the sake of clarity, the jacobi coordinate  for  the generic
molecular AB-X  system  is:
(r,R,theta), where :
r is the AB bond distance,
R is the distance of X from the AB CM,
theta is the angle defined by X,CM and B.
Now, the problem: Molpro make the calculation for theta=0 value and give
me an error after the z-matrix parsing if theta != 0.  Sure, there is a
problem with my z-matrix but I don't know where is it.
An output file that figures out the error is attached. Please, note also
that you can find an input example with a very similar z-matrix in the
Molpro user manual (p. 71) which is affected by the same problem.
Any advices are welcome,

Best wishes,

Mario Tacconi