PC GAMESS-related discussion club

Re: Symmetry Problem

Alex Granovsky
gran@classic.chem.msu.su

Are you using spherical harmonics? This problem can be due to quasi-linear dependences in the AO basis set, if not. In any case, you can try to add the following line to your input:


$moorth syms=1 symden=1 symvec=1 tolsym=1d-7 $end

to improve quality of almost everything related with orbital symmetry and to soften threshold causing PC GAMESS to abort job.

Hope this helps.

Best regards,
Alex

On Sat Dec 23 '06, Dong Xu wrote
--------------------------------
>I have an MP2/aug-cc-pVDZ job with the molecule being in C2h symmetry and it ran into this error:

> MP2 TRANSFORMATION CANNOT ASSIGN A DEFINITE ORBITAL SYMMETRY TO MO  278
> JOB ABORTS.  YOU MUST EITHER
>  A) PROVIDE A SYMMETRY ADAPTED MO SET BY GUESS=MOREAD
>  B) ENTER NOSYM=1 TO USE THESE SYMMETRY BROKEN MO-S.

>The problem is there are two 90 degree dihedral angles in this molecule (C2h symmetry) that I want to freeze throughout the calculation. If I assign NOSYM=1 to diable C2h symmstry, the optimization will turn the dihedral angles to 0 degree and find the global minimum. I didn't have this problem in my previous MP2/cc-PVDZ or MP/cc-pVTZ jobs.

>So, what's the best strategy here to finish this calculation and keep the geometry staying at this saddle point (two 90 degree dihedral angles)?

>Should I use RUNTYP=SADPOINT or IFREEZ/IFCART to freeze the coordinates, and how? I have COORD=CART, a full Cartisian coordinate geometry input.

>Thanks in advance and Happy holidays!

>-DX

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