[ADF-LIST] Vibrational Analysis in ADF

Alexei Yakovlev yakovlev at scm.com
Mon Jun 27 15:17:35 CEST 2016

Dear Yuming Sun,

On 24/06/2016 11:17, 孙玉明 wrote:
> Dear ADF,
> In the example Freq_NH3, there two types of Hessian matrix in TAPE21, 
> Hessian_CART and Hessian_complete, then which one should be used to 
> obtain normal modes and frequencies by diagonalization?
The Hessian_complete is completely internal to ADF and should not be 
used externally. The Hessian_CART is a Hessian matrix in Cartesian 
coordinates and it can be used externally.
> There is also a sub-section Force constants, what's difference between 
> Hessian Matrix and Force constants?
Also the Force constants is internal to ADF, it contains intermediate 
results from a Hessian matrix calculation.
> Is there any detailed instruction for frequency analysis in ADF?
Not that I know of, except for a document from Steve Wolff about 
analytical second derivatives but that one deals mostly with calculating 
the Hessian matrix.
> Another question is that when frequencies are calculated in Mobile 
> Block Hessian (MBH) model, no Hessian matrix in TAPE21 and force 
> constants are zeros. Although there are two references in ADFguide, 
> but how does ADF obtain normal modes, the force constants between two 
> blocks?
The method is published in JCP 126, 224102 (2007) and JCP 127, 164108 (2007)

I hope this helps.

Kind regards,

> Thanks
> Yuming Sun
> Yantai University
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