# Example: Numerical Frequencies, accurate Hartree-Fock: H2O¶

Download H2O_HF_freq.run

Example shows a Hartree-Fock frequency calculation with an accurate basis set.

The ‘DEPENDENCY’ key is set to 1e-4. Note that for hybrids and Hartree-Fock the dependency key is always set. The default value in that case is 4e-3. By explicitly setting the ‘DEPENDENCY’ key we can use a lower value, which is possible in this case. One should check that the results remain reliable if one uses a smaller value for the ‘DEPENDENCY’ key.

First a geometry optimization is performed.

$ADFBIN/adf << eor title accurate HF geometry optimization with large QZ4P basis set basis type QZ4P core None end adddiffusefit dependency bas=1e-4 ATOMS O 0.000000 0.000000 -0.007124 H 0.000000 0.751933 0.556531 H 0.000000 -0.751933 0.556531 END NumericalQuality Good xc hartreefock end geometry end end input eor mv TAPE21 t21  Next the frequency calculation is done. A restart is used to pick up the excited state geometry of the previous calculation. The orbitals are not read from the restart file (subkey NoOrb in the restart key). Also the fit coefficients are not read from the restart file (subkey NoSCF in the restart key). $ADFBIN/adf << eor
title accurate HF frequency calculation with large QZ4P basis set
restart t21 &
noscf
noorb
end
basis
type QZ4P
core None
end
dependency bas=1e-4
ATOMS
O         0.000000    0.000000   -0.007124
H         0.000000    0.751933    0.556531
H         0.000000   -0.751933    0.556531
END
NumericalQuality Good
xc
hartreefock
end
geometry
frequencies symm
end
end input
eor