Linear response

 

A well-known example of a linear response   function is the polarizability. A typical input for SCF static and dynamic polarizability tensors , given a few selected frequencies (in atomic units) will be:

**DALTON INPUT
.RUN RESPONSE
**WAVE FUNCTIONS
.HF
**RESPONSE
*LINEAR
.DIPLEN
.FREQUENCY
 3
 0.0 0.5 1.0
*END OF INPUT

The .DIPLEN keyword has the effect of defining the A and B operators as all components of the electric dipole operator.

The linear response function contains a wealth of information about the spectrum of a given Hamiltonian. It has poles  at the excitation energies , relative to the reference state (not necessarily the ground state) and the corresponding residues  are transition moments  between the reference and excited states. To calculate the excitation energies  and dipole transition moments  for the three lowest excited states in the fourth symmetry a small modification of the input above will suffice;

**RESPONSE
*LINEAR
.DIPLEN
.SINGLE RESIDUE
.ROOTS
 0 0 0 3
*END OF INPUT