Calculation of analytical second derivatives is requested by specifying
in the main ADF input.
A high accuracy is specified for the numerical integration to be sure of reliable results. In general, it seems advisable to use high accuracy for heavy nuclei at the moment, whereas default integration accuracy is usually sufficient for light atoms. Further, high integration accuracy is more needed in the atomic spheres than in the rest of the molecule. A cost-effective solution may therefore be to specify a higher integration accuracy in the spheres only (using the accsph subkey of the INTEGRATION keyword).
$ADFBIN/adf << eor title CN atoms N -1.3 0.0 0.0 C 0.0 0.0 0.0 end Basis Type DZ Core None End charge -1 XC LDA Xonly End integration 6.0 AnalyticalFreq End End input eor
After SCF is completed, the energy second derivatives matrix is calculated and analysed, which yields in this case one frequency.