Symmetry specification for linear molecules

[Aqsa Zahid Shaikh]

Hi all,
I am trying to run a linear molecule eg, OH with d2h symmetry, by defining as follows:

SYMMETRY,X,Y,Z

angstrom

r = 0.97

geometry={

2

OH

O  0.0 0.0 0.0

H  0.0 0.0 r

}

{rhf

wf,7,5,1

occ,2,1,1,0,1,0,0

closed,2,1,1,0,0,0

print,orbital=3

orbital,4202.2

}

I get the following error:

 Because of noorient option, program will not align to your requested symmetry elements

 Try again with different symmetry request

 This error can also happen in geometry optimizations that specify symmetry-breaking internal coordinates in terms of active variables

 User-specified symmetry elements: X,Y,Z

 Symmetry elements: X,Y

 ? Error

 ? Symmetry error

 ? The problem occurs in zmatrix.f:zmat_evaluate

When I run the same molecule with c2v symmetry. It does the calculation as intended.
According to molpro manual, a linear molecule can be defined either by d2h or c2v geometry. So I am a little puzzled as to why does molpro enforce X,Y symmetry on the molecule.

Any suggestion on how to implement d2h symmetry for OH will be very useful.

Thank you.

[peterso...@gmail.com]

A linear  molecule with D2h symmetry requires a center of inversion, which OH does not have.

 

Regards,  -Kirk

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[Aqsa Zahid Shaikh]

Thank you for the clarification. I was wondering on similar lines. So in this context can only homonuclear molecules be defined by d2h? And all hetero nuclear linear molecules use c2v?

[peterso...@gmail.com]

A little review of group theory would be of interest to you I think.  A linear molecule such as acetylene (HCCH) has D2h symmetry.

 

Regards,  -Kirk

[Aqsa Zahid Shaikh]

Thank you for the information. It makes sense now. Thank you.

[Martina Kaledin]

OH linear molecule and is  of C_infinity_v point group symmetry and C2v is used in Molpro. Homonuclear diatomics would be of D_ infinity_h and D2h is used. For reviewing molecular symmetry, I use 

https://symotter.org/ website. This is a fantastic resource for students and whoever needs to refresh molecular symmetry. 

To view this discussion, visit https://groups.google.com/d/msgid/molpro-user/CALQAJ1mOuGC%3D-m0-CQtiADcFGk4H8miYMKFa7-u-fpJD%2Bz1J-Q%40mail.gmail.com.