Linear Response

Instead of performing two explicit displacements one can use perturbation theory and compute the second derivative from the linear response of the system to an infinitesimal replacement. This cuts the number of calculations in half and avoids errors due to taking numerical derivatives. This option is not implemented, e.g. for k-points or the Hockney poisson solver.

&CPMD
  VIBRATIONAL ANALYSIS LR GAUSS
  RESTART WAVEFUNCTION COORDINATES
  CONVERGENCE ORBITALS
    1.0e-7
&END