Electronic spectra

Electronic excitation energies can be calculated using the keyword ELECTRONIC SPECTRA in the &CPMD section. This calculation is performed in three parts. First, the ground state wavefunctions are optimized, then a limited set of unoccupied orbitals is determined and finally the TDDFT response equations are solved. A typical input for such a calculation would look like

&CPMD
  ELECTRONIC SPECTRA
  DIAGONALIZATION LANCZOS
  COMPRESS WRITE32
&END

&TDDFT
  STATES SINGLET
    5
  TAMM-DANCOFF
  DAVIDSON PARAMETER
  150 1.D-7 50
&END

For this calculation of the electronic spectra defaults are used for the ground state optimization (ODIIS and $10^{-5}$ convergence). The calculation of the empty states is performed using the Lanczos diagonalizer with default settings. The final wavefunction will be stored in the restart http using 32 bit precision.

Five single states with the Tamm-Dancoff approximation have to be calculated. The parameters for the Davidson diagonalization have been changed to 50 for the Davidson subspace and a convergence criteria of $10^{-7}$ is used.

Restarting this type of calculation has to be done with care. At the end of each phase of the calculation a new restart http is written. If the defaults are used, each time the http RESTART.1 is overwritten. For a restart from converged ground state wavefunctions and canonical Kohn-Sham orbitals a restart with
RESTART WAVEFUNCTION COORDINATES
will be used. A restart also including the linear response orbitals will use
RESTART WAVEFUNCTION COORDINATES LINRES.
In this case only restarts from the http RESTART are possible as after phase one and two the http RESTART.1 would be overwritten and the information on the linear response orbitals, read only in phase three, would be lost.