[molpro-user] Symmetry in Optimizations

[Doran Bennett]

I have recently been trying to perform a geometry optimization on a 
molecule with Cs symmetry. I am using UCCSD(T) calculations, so the 
geometry optimization requires numerical gradients to be calculated. If 
I run the optg command without specifying anything else the calculation 
crashes when it tries to calculate the numerical gradient of the 
dihedral angle (since this clearly breaks the symmetry of the molecule). 
I have also tried running it specifying symmetric displacements with

> {optg,saveact=1_cc_cis_mcf.geom;                                                                                                                      
>  
> coord,zmat,sym;                                                                                                                                       
>  
> } 

However, the calculation crashed then with the error:

> PROGRAM * OPT (Geometry optimization)     Authors: F. Eckert and H.-J. 
> Werner
>  
>  ? Error
>  ? Unknown option on COORD directive: SYM
>  ? The problem occurs in Opt_inp
>  
>  ERROR EXIT
>  CURRENT STACK:      MAIN

Does anyone know how to convince the numerical gradients to use 
displacements that will not break the symmetry of the molecule?

Thanks,

Doran Bennett
University of Chicago