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

mario tacconi at caspur.it
Mon May 2 13:00:04 BST 2005

Dear Dave,

I' ve just tried your double-dummies-Z-matrix and it works very well at 
every theta angle value!
Thank you very much!


>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:
>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
>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

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