[molpro-user] Symmetry in Optimizations

[Kirk Peterson]

Doran,

the key is not to have variables in your z-matrix that can lead to  
symmetry breaking OR use the inactive subcommand of optg, ie.,

in the z-matrix in your case, put in an explicit 0. or 180. for your  
dihedral angle or

optg;inactive,dihedral_variable;


-Kirk


On Apr 24, 2006, at 12:08 PM, Doran Bennett wrote:

> 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
>
>