## Firefly and PC GAMESS-related discussion club

Learn how to ask questions correctly

** Re: hessian_asymmetry **
Alex Granovsky

gran@classic.chem.msu.su

Dear Richard,When computed semi-numerically (i.e. using finite differences of

analytical gradients) or fully numerically, resulting hessian matrix

is not exactly symmetric as it should. SYMFCM checks for this

asymmetry and prints pairs of Cartesian coordinates having largest

asymmetry. This asymmetry is the measure of a numerical noise and

anharmonicity. One may check for largest absolute asymmetry and

ensure it is not too high (say, less than 3d-3 or so). If asymmetry

is high, the quality of frequencies is questionable.

Kind regards,

Alex

On Tue Sep 2 '14 3:48pm, Richard wrote

--------------------------------------

>Lines such as

>SYMFCM: LARGEST HESSIAN ASYMMETRY: PAIR # 1: I = 15 J = 12 REL. ASYM = 0.2210484995D-02 ABS. ASYM = 0.2920159034D-04 etc.

>are printed after a hessian calculation.

>Is there any useful information here, maybe about the reliability of the frequencies?

>Richard

Tue Sep 2 '14 6:40pm

This message read **583** times