# Example: TDHF excitation energies: N2¶

Download N2_TDHF.run

Calculation of the excitation energies of N2 using time-dependent Hartree-Fock (TDHF). It also shows the possibility to use the Tamm-Dancoff approximation (TDA). This examples consists of 4 calculations:

• non-relativistic TDHF
• spin-orbit coupled TDHF
• non-relativistic TDHF, TDA
• spin-orbit coupled TDHF, TDA

The results will be inaccurate due to small basis set. The key ADDDIFFUSEFIT is required for a more accurate fit of the density.

\$ADFBIN/adf << eor
Atoms
N 0 0 0
N 0 0 1.0977
End

XC
hartreefock
end

dependency bas=1e-4

Basis
Type DZ
Core None
End

BeckeGrid
Quality Good
End

excitations
lowest 5
end
End Input
eor


In case of spin-orbit coupling one needs to include the key RELATIVISTIC with argument ZORA SPINORBIT. In practice one needs to calculate more excitations if one includes spin-orbit coupling, since the singlet-singlet and singlet-triplet excitations are not calculated separately, but will be treated simultaneously, since they may mix.

excitations
lowest 20
end
relativistic spinorbit zora


The Tamm-Dancoff approximation (TDA) will be used if one includes the key TDA. The calculation is then effectively a CIS calculation.

TDA